GG,
Here are a couple of things you can try (used to work in Win2k - don't know about XP cuz I've migrated to linux)
Get a copy of regclean from MS' site (or pm me and I can send a version that works from 95-2k). Run regclean until no more problems/errors show up (alternatively, you can search for any registry cleaner - they should all work basically the same).
You can also try to increase your swapfile and registry sizes. To do this in 2k (XP should be similar), right click My Computer, go to Properties, click the Performance Options button, and the Change button. I would recommend 2x your physical memory for your paging memory (swapfile, virtual memory, etc.), and 2x your current registry size for the maximum registry size.

A note of warning here (learned the hard way from 2k, 2ksp1, and 2ksp2 which precipitated my migration to RedHat linux): Chech your registry size regularly - especially before installing any new applications. If your registry size is approaching the max size limit, you run of the risk of your registry getting compressed to fit in the maximum size allocated which in my experience trashes the registry. This was a known bug in 2k that was supposedly fixed in sp2, but I can verify that the problem still exists, and since XP is based on the 2k kernel, I would suspect that the same holds for XP as well.

Anyway, the trick is to keep your registry and swapfile as lean and clean (and defragged) as much as possible. The available defrag utilities and registry cleaners should do just that and keep you from having to 'restore' your system.

Cheers,
Bob