www.themexp.com has some good themes. There's also several other programs out that act as a replacement UI for XP (if that's what you're running), though I've found they eat resources. I liked the Longhorn one, but didn't reinstall it after my last format since it seemed to slow things down a bit.
Or, you could just make your own, or beg someone to photoshop one for you.
How Much Horsepower Can I have And Still Go To Heaven?