I want to make my fireball cube texture into hammer, but I don't want to have to replace any other textures. the Propper tool isn't creating anything for me, even when I use it for portal 1. the texture I am trying to use is this: http://i.imgur.com/alpLj.png

If anyone here can get this as a new cube texture or even a whole new model that works in game, then I thank you.

If they can't then I'm doomed.

you have to decompile the cube model with a decompiler, google it "mdl decompiler".
Then use that skin as a vtf for it.

thank you! but then how do I get it back into the game as a new model?

also, the MDLdecompiler is not working. it keeps bringing up this: http://i.imgur.com/gY7bc.png

(I am very new at mapping and stuff over here.)