so what happens when u try to go into safe mode? That's your best shot me thinks, then do a system restore. Nother option is to boot off of "your" XP CD and reinstall/repair. Dunno, sounds like it's time to format c: If you want to give SP2 a go agian (i know it's crazy) uninstall any Virus Scan progs and Firewalls first. Then install afterwards. Also take a look at the list of "bad" apps for SP2 just for kicks:
http://support.microsoft.com/default.aspx?kbid=842242