Nice checklist, one thing to add though...
Have your XP disk and application disks ready, and back up your data completely before starting. That way, even if XP SP2 hangs on restart, you'll lose no more than time as you wipe your drive and reinstall XP with SP1 clean, then your A/V and firewall, then install SP2, then all your apps and data...
If it works, you just got prompted to make a decent backup, so you benefit anyway.
