Personally system restore in XP is pretty poor, it isn't close to 100% and often has unforeseen consequences. Mainly because it doesn't cover everything and occasionally a restore point fails, regardless of avast self-defence.
That is why I have been using Hard Drive imaging software for almost as long as I have had XP. This provides a robust backup and recovery strategy (weekly imaging of a drive and I keep the last 6 versions of the backup) which XP system restore can't come close.