Oh dude, i'm begging you. You do not want to go through the sh*t i had to go through. There are some trustworthy sites out there, and there also those sites that put a POS gaelicum.A virus on a computer that u just reformatted, and you need another reformatt to get rid of the SOB.
The themes that i have tried, and that work, virus free:
Royale Noir
Royale
Windows Zune Theme, off the microsoft website
^^^^^^Those three are extremely nice themes that work without any bugs on my system.
http://www.tune-up.com/download/
-This is a link to TuneUp Utilites 2008, it lets you tweak alot of you windows GUI. In it, there is a visual style program, that links you directly to Tuneup Utilites Theme database, and you pic and chose to your liking. These themes aren't all that smooth looking to tell the truth, but w/e.
Anther way is to patch your UXtheme.dll,
http://www.softpedia.com/get/System/OS-Enhancements/UXTheme-MultiPatcher.shtml, and from there you can download themes off the net <how i got my ass in trouble>.
I would stick with he first three.