TexDXT you should have gotten with the editor. You need to download texture tools. Here's excerpt from an old release log:

I saw the TexDXT in the bin file already, but the error is still there: "Failed to load TexDXT.dll".
There isn't a TexDXT .dll in the bin folder of Texture Tools, and the one that came with TTP didn't work either, so I used SS3's TexDXT (this didn't work either).

http://i.imgur.com/9a9R6Qc.png There ya go. There's a lot wrong with that image, and that trollface is supposed to be for Floor 4-2.

Whoa-ho! I think I found out how everyone else did it. Dangit Solais! You told me to put it in a 2^n dimension, when that itself was the problem >_>

Anyway: the solution is to make your picture not 2^n numbers (2x2, 4x4, 8x8, 16x16...) so that the editor doesn't automatically compress your picture. Yeah, it's roundabout!

It says it cannot load TexDXT.dll because that dll depends on other dlls in texture tools, and that probably wasn't installed into your path. If you put all the texture tools dlls in the game's Bin folder, it might solve the problem.

Well, I also said that using not 2^n numbers can cause crashing problems with others, especially those using the Direct3D 9 API, this is why it's not recommended.

And yes, what Alen said. For example, this is how my Bin folder looks like: http://i.imgur.com/3w9BeEX.jpg