Maintaining the Registry
The Registry is mysterious, much like physical ailments. There are countless snake oil salesmen out there to take advantage of the afflicted. All sorts of Registry programs are breathlessly offered on the Internet. Most of them are more hazard than help.
Registry Cleaners:
I've tried several Registry cleaners, and I only recommend two, which are essentially the same one. RegSupreme or the cleaner in the jv16 PowerTools utility package from Macecraft are the Registry cleaners that I trust. The predecessor of these cleaners has been around -- and highly regarded -- for years. First as free utilities, and now commercial.
One trouble with Registry cleaners is knowing what to let them fix. There are usually hundreds of things that they find, and for most of them it's not clear what will happen if you let the cleaner remove/fix them. I trust the Macecraft cleaners to get it right because the originator knew what he was doing.
Registry Compactors
You can find programs to defrag/compress the Registry. I have used them, but there is not much need to do so under ordinary circumstances.
If you're an average user, your Windows XP Registry will probably still be OK if you never clean it up or compact it. :-)
