While it isn't the complete answer, and it can be dodgy if you don't know what you're doing, using a proggie like RegClean or RegMaid to troll through the registry and find dodgy or unused entries might be useful.
The only caveat is that you have to be really, really careful, cos playing with the Windows registry can lead to a lot of problems if you're not sure what you are deleting/changing.
RegClean is a free microsoft product, and I think you can get RegMaid from CNet or Shareware.com
- gaffa