Its almost impossible (well ok quite hard) to automatically see what keys a program is using., you can see which ones it used when it installed with cleansweep or such.
You have to actually hook the program and watch it accesssing
regmon from
www.sysinternals.com will handle it.
some reg cleaners will really screw up your system, since they assume a lot about file paths, some programs use environment variables in their registry keys and teh reg cleaner will think its a bad path and remove them, so make sure you use one that has an undo
