Winoscentral have got their hands on the lastest version of RegCleaner and it works with Windows XP.

Here's what's new

Remove file types
Remove entries of old software
Uninstall and remove Software from the add/Remove list
Remove unused DLL files
Remove unused Shared DLLs (Automatically detected)
Automatic backup feature

Download RegCleaner - v4.3.0.780 for Win95, 98, 98SE, ME, 2000, XP, NT4 Rancho*: Actually this version is not new but apparently it also works for WinXP...