Google is your friend. Fix for that error is here:
http://www.tech-recipes.com/windows_tips556.html
Fair warning: SP2 upgrades can go badly unless your system is CLEAN. To ensure a problem free install, temporarily disable any unusual background applications. Unplug ALL USB devices, disconnect ALL printers.
It's IMPERATIVE that there's no Spyware on your system. Due to the security features of SP2, if it's installed on a system with spyware, you will not be able to boot into Windows. I've seen this happen a lot. You then have to do a manual registry restore in order to boot into safe mode to use system restore.
Please follow my detailed spyware removal instructions here before installing SP2:
http://theflyingpenguin.com/spyware-removal.shtml
Also, I would highly recommend you run a FULL virus scan in SAFE MODE.
Backup your critical data just in case.