Unless you have a specific problem you're trying to correct, it's best to stay out of the Registry.
Registry cleaners mark entries as bad, depending on what the software creator thinks is bad.
That's why no 2 cleaners will find all of the same "problems".
Registry "problems" actually have very little effect on the overall performance of the operating system.
Please see this article:XP Fixes Myth #1: Registry Cleaners
Improper changes to the registry could render your computer inoperable.Remember to backup the registry before making any changes.
Instructions, on how to do that, can be found here:How to back up, edit, and restore the registry