I feel your pain, my new XP just started freezing up from time to time, and for the life of me I can not figure out why. I've uninstalled EVERYTHING, and it still freezes! It started freezing when I was checking out virus software. And I think the uninstall did not uninstall some invisable service that scans my stuff. Might be totally wrong about that since I can get any meaningfull info from task manager or msconfig. A Unix ps with proper arguments would tell me what I need to know.
Possibly a hook, rather than a service. I would use the XP rollback feature and restore the OS to an older time when it worked.