I installed SP2 with Norton Internet Protection and had to unistall SP2 because it slowed my computer down.
Norton is a resource hog.
Except for anti-virus, get rid of Norton. Don't go without XP SP-2, a lot of security updates require that it be installed first.
Had an IT guy work on my machine to find out why it stalled when we had network problems. After fixing broken dll files, reinstalled SP-2 and something like 60 MS security updates were downloaded.
My bottom line is that with Windows firewall (comes with SP-2), antivirus, and a couple of free anti-spyware/adware programs, the computer works just fine.
That's when I noticed it really slowed down. Plus I'm having other issues with windows (since the downloads) but Microsoft won't respond to my complaints until I give them $35.