Should I upgrade my OS from Windows Vista to Windows XP?

I would keep Vista if your computer can run it or better yet, upgrade to Windows 7 if you can afford it. Whatever you do, I wouldn't put XP back on the computer as it's too old and it's going to lose support for security patches in April 2014. Going back from Windows 7 or Vista to XP is like going back from Xp to Windows 98. I know that all the earlier Windows versions usually use less resources than the newer and later versions. But if all you want if something that isn't a resource hog, you might as well be running Windows 1.0.