System restore would normally be a fall-back position if things went wrong.
Be careful using RegSeeker. It is a good program in the right hands, but it can cause some programs to become inoperable, requiring a re-install to to repair. For example, it totally screwed up my installation of Office 97, but only because I was vicious in deleting entries.
It does backup as a default, so providing you can re-open RegSeeker, you can undo any changes the program has made.
If you are unsure about the registry, stay clear, but if you want to try and use the program, for starters, until you find your way around, just delete the entries marked GREEN and you can't go far wrong.