First, you need to download the 64-bit files available here:
http://community.pcgamingwiki.com/files/file/163-unreal-tournament-2004-64-bit-windows-binaries/



Save it anywhere you wish, Windows will be able to open the file without needing any third-party programs (don't worry, the steam version of UT2004 already uses the latest patch so patching it isn't neccesary).

Now, open up the archive you just downloaded, and extract it's contents (except the readme file, that one isn't needed) to your Unreal Tournament 2004 folder (should be located in "C:/Program Files (x86)/Steam/steamapps/common/Unreal Tournament 2004).


This one:

Now, here comes the slightly tricky part. You'll have to rename the 64-bit file into the name of the 32-bit file. This way, steam will actually launch the 64-bit exe when you start the game.

First, find these 3 files:

UT2004.exe
UT2004.ini
UT2004.log (NOTE: This file will only be created if you launched the game at least once, and i'm unsure if it even needs to be renamed. To be on the safe side, do it).



And rename them. It can be anything you want, but for convenience put old next to their filenames. Then, find the 64-bit executable named ut2004-win64.exe and rename it to the former name of the 32-bit executable.


Now, try to start the game through Steam. If you did everything correctly, you should now be able to play Unreal Tournament 2004 in 64-bit mode, complete with the Steam Overlay.

If you find the regular splash picture appearing before you launch the game now confusing since you made the 64-bit exe work with steam, here's a way to fix it.

Go to your Unreal Tournament 2004 folder in the steamapps folder. From there, enter the Help folder. Find a file named UT2004Logo.bmp and rename it to whatever you please, but like with the 32-bit exe files, i recommend putting an old after the filename.


(Yes, it didn't preview for me, sorry about that)

Then, find the 64-bit splash image. It should be named UT2004-Win64Logo.bmp.



As with the 64-bit exes, rename the image to the former name of the 32-bit splash image, that is UT2004Logo.bmp.

The next time you start the game through, it should display the 64-bit splash image.

And that's all for this guide. I hope it helped you with running one of the best MP FPS games ever released, with 64-bit support AND steam overlay.