The main reason for going for XP SP2 is if you do not have a firewall. It adds it's own version of internet security and pop up window restrictors as well. If you have something like ZoneAlarm, you hardly need to mess with this update - certainly not until Bill Gates has sorted this mess out.
A word of warning to anybody developing sites for customers that use popup windows (never a good idea anyway) but this XP update will block these if they are automatically generated.
Good luck - Steiner
Condottiero - Freelance Multimedia Design