[RECOMMENDED] There are a couple of typos and formatting issues (such as the lack of a space after a couple of commas) in the various hints that appear during loading screens.

• To fix this, download this text file:
  http://gourl.gr/b45a
  move it into the folder:
  ...\Steam\steamapps\common\divine_divinity\localizations\english
  and replace the file that was previously there to fix this.

[INFORMATIVE] There are a lot of quests that if carried out in a certain way will block other quests' progress or won't be able to be completed. A user was able to list all known bugs and made a Steam guide:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=233403473

[NOT RECOMMENDED] One way to solve all the compatibility issues listed below, is to use a program such as VirtualBox that creates a virtual operating system in which you can play the game without all the glitches it comes with, when played on Windows Vista, 7,8 and 10.

• You can download VirtualBox here:
  https://www.virtualbox.org/wiki/Downloads
  The way this program works is that it assigns a portion of your hard drive memory and some of your CPU cores to run a supplementary Operating System alongside the primary OS where you can run old software such as this game that wouldn't work otherwise.
  The recommended OS to run this game on, is Windows 98/Me

Windows XP, let alone 98/Me, don't support Steam. So you probably need to copy all the game's files from:
\Steam\steamapps\common\divine_divinity
and somehow paste them into the virtual machine's Operating System. I, however, have never tried this method myself and have no idea if it would actually work without Steam or if you would need to buy (or download) another copy of the game outside of Steam.

[INFORMATIVE] The base game's options configuration (by choosing Configure at the start of the game or by starting the file "configtool.exe" in the main folder of the game) offers few selections but some may bring up graphical or compatibility issues, so they need to be understood.

• Software/DirectX are discussed in greater detail later in this guide.
  
  
• Resolution refers to the in-game and window resolution of the game.
  640x480, 800x600 and 1024x768 are the resolutions in which the game originally ran and they're also the only resolutions that won't black bars around the main menu. If the game closes itself upon starting it, lowering the resolution might fix this.
  
  
• AlphaBit was used, when the game originally came out, to correct the "rainbow effect" that appears when the Operative System doesn't support 16bit color depth (which highly saturates the screen and distorts colors). It currently serves no function but to make that same effect that used to fix appear. It also doesn't solve the "rainbow effect" that appears when patching the game for DirectX (later in this guide). So keep it disabled at all times.
  
  
• Smoothness has a currently unknown effect, it probably just softens a bit the edges of the models at the expenses of a minor drop in performance. Both are so negligeble that it's useless to debate the worthlessness of enabling this option. Leave it on if you like slightly better graphics, turn it off for a fraction of FPS more.

DirectX maintains all the original games' 3d features at the expenses of huge framerate drops and when combined with a high resolution it usually makes the game unplayable.

• [RECOMMENDED] One quick way of fixing this is to use the Software mode that you can find in the Configure option, when starting the game, or by starting the .exe file "configtool" in the main folder of the game. This configuration however disables all the 3d features the original game had (all water reflections animations, fog and fog of war "volume", no fading out for NPCs that disappear outside the screen,...). This is the only method that let's you play at the highest resolutions and at the highest FPS without other complications (all the other methods listed below require very low resolutions and most of the time have stutter problems regardless or create other bugs), so even if you're looking for something that gives you an authentic experience of the game you shouldn't be so quick to discard this option.
  
  
• [NOT RECOMMENDED] Another fast way of solving this issue is by downloading this .zip file:
  http://data.4w.io/divinityfix.zip
  or its .7z counterpart:
  http://data.4w.io/divinityfix.7z
  containing 3 files of a fanmade patch, an "install.bat" file that installs the patch, an "uninstall.bat" that uninstalls the patch and a "divinity.sdb" that is the patch itself. Start the "install.bat" file and once it finishes, close the Command Prompt by pressing any key, the installation will work wherever you put the files, so long as they're all in the same folder. This method tweaks most of the game's 3d features (so it won't be a 100% true experience of the original game either) in order to lower the performance demand, which raises the FPS even for low-tier PCs, but it will also corrupt the CGI cinematics (there are three of them in the game, one in the main menu, one during half-game and one at the end of it) and the Save/Load "thumbnails" with the same "raibow effect" for when AlphaBit is enabled.
  
  
• [RECOMMENDED] A third solution is to download WineD3D:
  https://fdossena.com/?p=wined3d/index.frag
  extract the 3 dll files "ddraw", "libwine" and "wine3d" and place them inside the main folder of the game. This fix tweaks the 3d features of the game enough for the game to be playable, but less than the method above in order to maintain the integrity of the original game's experience. This however means that the amount of performance demand is still high and any resolution above 1024x768 (tested with a Nvidia 1080GTX) will make the game stutter again. The game will also behave strangely towards the "Alt" key (only the left one), which should just highlight interactable objects. It will instead pause the game too upon releasing the button, but only if the player didn't move after being pressed.

[RECOMMENDED] Using the second method (this is useful only if you use that fix) described above, you can use a program called dgVoodoo 2 to enhance the internal resolution further than whatever you chose in the configtool.exe file (or add Anti-Aliasing, Texture Filtering, Vsync,...).

• Download the program at this link:
  http://www.dege.freeweb.hu/dgVoodoo2/dgVoodoo2.html
  You don't need to download any other file other than the program itself so don't be bothered with what the site says. Extract the files "dgVoodooCpl.exe" and "dgVoodoo.conf" that are in the main folder and the 3 dll files "D3D8", "D3DImm" and "DDraw" that are in the folder called "MS" and put all 5 files into the game's main folder that's in:
  \Steam\steamapps\common\divine_divinity
  dgVoodoo is now installed and to change its options you only need to start the file "dgVoodooCpl.exe". In the General tab you can choose options to change the game's window (aspect ratio, saturation, brightness, size,...), skip the Glide tab because it's options are only useful if you use the Glide configuration (which is available only if you use the old "configtool.exe" from the original game) and finally in the DirectX you can choose options to change in-game features (such as internal resolution, texture filtering, anti-aliasing, VRAM,...).
  If you don't understand what a certain option does, check the guide on the official dgVoodoo site:
  http://www.dege.freeweb.hu/dgVoodoo2/QuickGuide.html

[INFORMATIVE] You can use dgVoodoo, even if you didn't choose the second way of dealing with DirectX 9's performance demand, if you need to resize, recolor or fix the game's window. But you must not put the 3 dll files, that are in the folder "MS" of dgVoodoo's zip file, in the game's main folder and you must select the option "Disable and passthru to real DirectX" in the DirectX tab. Be careful when using it this way though because it may generate undesired effects due to software conflicts and should be therefore avoided unless absolutely necessary.

If you adopted the third method to deal with DirectX performance issues, you'll have to solve the problem with the left Alt key pausing the game, as well.

• [RECOMMENDED] A first solution is to simply use the right Alt key (also known as AltGr) instead of the left one. In the game they serve the same exact function, except for the fact that the right one isn't bugged. Outside of the game, the only difference I've noticed is that the right Alt key (AltGr) doesn't immediately open the window you've selected when using it in the combination Alt+Tab.
  
  
• [RECOMMENDED] Another way of fixing this is by mapping the right Alt key onto the left one and you can do that (without having to manually open another program everytime you want to play Divine Divinity or to see it pop up everytime you start your PC) by using this keyboard remapping program:
  https://atnsoft.com/keyremapper/
  First of all click on Tools, then Options and uncheck "Show icon in the taskbar" so that it doesn't bother you when it launches when the Operating System is started. Then add a key remapping, click the left Alt in the first box, the right one in the second one and uncheck all checkboxes under. Ultimately, click on the first icon that says "add an exception" next to the "Apply" box, launch Divine Divinity, select "Add" and "Launched applications", then select Divine Divinity, confirm all the opened tabs and "close" the application (clicking on the exit button merely reduces it to the tray bar).
  
  
• [NOT RECOMMENDED] If you don't like the fact that the free version of Key Remapping only lasts for 30 days, there's a program called AutoHotKey:
  https://www.autohotkey.com/
  that lets you write scripts in a proprietary scripting language that allow you to do all sorts of things, included remapping your keyboard. Once you've installed it, download this script:
  http://gourl.gr/b45b
  and place it in the folder:
  \Users\<User_Name>\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup
  where instead of <User_Name> you put your user's name.
  The program will now launch itself everytime you open Windows (if you want it already open because you already want to play the game, just start the script by double-clicking on it or restart your PC), but it won't display any additional icon in the tray bar, nor will it be as heavy on the startup as an entire program when using the method above, this one however, won't attach itself to the window itself but will only check if it's active or not, so since the game takes some time to become inactive when Alt+Tab is used, the script will continue working for 10-20 seconds after changing window. Closing the window instead has an immediate effect.
  
  
• [NOT RECOMMENDED] Finally, if you want a permanent solution and don't care about the differences between the two Alt keys outside of the game, you could choose to use SharpKeys that you can download here:
  https://www.randyrants.com/2011/12/sharpkeys_35/
  SharpKey is a program that permanently (unless you revert it back) remaps your keyboard inputs by making changes in the Windows registry so that you don't have to manually open another program everytime you want to play the game or without having a program opening in the background at every startup. Until you change it back, your left Alt key will perform like a right Alt key even outside of the game.