STRONG ADVISORY: No matter how safe and sound the method, or who suggests it to you, it is always smartest to backup the Windows Registry before attempting to make any changes in it!
Unfortunately (and contrary to the situation in Windows 98 and ME), there is no native tool for compacting the Windows 2000 or XP Registry. The good news, though, is that
In the first year and a half of using Windows XP, field reports and personal experience agree that Registry bloat is not really an issue in Win XP — at least, nothing close to what it was in Windows 95, 98, and ME. Windows 2000 really doesn’t show this as a problem either.
Nonetheless, Registry bloat may be an issue in a particular Windows 2000 or XP installation, so it is helpful to have a way to compact the Registry. The tool is NTRegOpt by Lars Hederer. I recommend that you also download another of Lars’ freeware offerings, ERUNT, which lets you efficiently back up the Windows NT, 2000, or XP Registry — and comes with NTRegOpt bundled in.