I've recently came across , thanks to a friend , on a guide showing you how to change the XP look of you're PC to Vista or Windows 7 or any other custom theme you can find.Here is the guide How-To: Use unsigned themes on Windows. For themes and things like this go to http://customize.org/.
Here's a pic ( I got Windows XP SP 3 right now )
If you can't get this to work or need help just ask in the thread and I will reply.