RegCleaner not RegClean works quite well being a freeware found at
http://www.dewassoc.com/support/useful/regcleaner.htm After trying several like RegCure and others that one still remains the best all the way from 95 to Vista!
For various "tweaks" and fixes an old 2003 registry guide works quite well for modifying the system registy in Windows. This however is not for use in Vista there. At one time you could even download a free copy of the guide where now you are limited to viewing the guilde while on the pages.
http://www.pctools.com/guides/registry/
One thing to note there however is you edit the registy at your own risk! You have to follow the instructions completely. As far as any modifications you are on your own there since that's not a topic for discussion here.
Another tool found removing a specific reg value and even seeing a specific driver removed from the system32 folder is the RegSeeker tool found at
http://www.hoverdesk.net/freeware.htm If you have a bad install of a program or update that can be a big help at times.
One method for seeing a performance leaves out the need for anything more then simply cleaning up leftovers often found when uninstallers tend to leave "orphans" behind as the term there. The msconfig utility is one tool where you can undo any mistakes if you end up disabling the wrong item like an essential background service. Besides the startup group the option to "hide all Microsoft services" box is checked off before entering the services tab there.