If your running Win2000 or XP, Just put the CD in and 'fix a damaged installation.' It reinstalls all system files to their original versions.
Win98? Unless you can find the .dll that's doing it, you might as well wipe out the partition and reinstall windows. It will save you hours.
Just make sure when you're done to install Moz/Firefox and then hide all associations to IE so they can't use it anymore.
:-D
