well that error is a broadcom application thing so im thinkin it got corrupt somehow and if you can get in using safemode then try restoring to a before point or running scans as above said.
if that fails it seem to me your simplest option would be a system repair.
assumng you have an XP disk
1. Boot up your PC with the XP cd in the drive.
2. When prompted press enter to boot from CD
3. XP should now start to load a couple of files
4. You will then be prompted with a blue screen "Welcome to Setup"
5. Press enter (although repair is an option here you dont want this as its for more advanced use)
6. Press F8 to agree the license agreement
7. Now hopefully you should be able to see something along the lines of
C:\Windows "Microsoft Windows XP"
8. Make sure its highlighted and press "R" to repair.