Problems after infection with Spy Defender Pro

I think I got an infection when SpyDefender Pro showed up on my XP computer. I think I got rid of it, but now Internet Explorer doesn’t work right, I can’t open System Restore (even in safe mode from the command prompt), and Windows update doesn’t work. Also, the Search program doesn’t work. I assume that there are still corrupted files somewhere. Any simple fixes?
Interestingly, Firefox works.
Thanks.