I know this thread is ye olde, but since AMD seemingly doesn't give a damn about XP users, the link jimmysmitty posted gives out this:
http://img203.imageshack.us/img203/3115/yayforamdsupport.png
As I couldn't find that exact same driver anywhere else, I went through the effort of uploading three mirrors of that installer, making an account here and posting them
http://www.mediafire.com/?z8bo9s5jka6b5zn
http://filesmelt.com/dl/AMD_processor_driver_for_XP_only.exe
http://www.gamefront.com/files/22643180/AMD+processor+driver+(for+XP+only).exe
Gamefront will mess up your download if you live on any of the countries on their "blacklist" though. (About half the planet outside the US)
I really hope I'm not breaking any rules with this, but if this site's rules are common sense stuff like they usually are this post should be fine.