Hello Jar_
The only time I've heard of any troubles like that occurring is when SP2 is installed via Windows Update with the antivirus program running. Could it have been anything to do with that? Norton suffered a bit when installing SP2 this way. Downloading the complete SP2 file (or obtaining a CD) and installing it with the antivirus program and firewall turned off is now generally recognised to be the best way to do the upgrade.
Windows Updates should be kept up with to avoid security troubles, so it would be best to try and resolve the problem with Windows Update and McAfee no matter what caused the trouble. How about reinstalling McAfee? That might work. Also, a visit to the McAfee site and a read of any FAQ sheets they have might be worth a try. Perhaps even ask about this in their support forum.
http://forums.mcafeehelp.com/index.php
Another good precaution would be to scan the system for spyware and viruses. Since you can't use your own antivirus program at present, use an online virus scanner. Perhaps this one:
http://housecall.trendmicro.com/
Typing
online virus scanner into a search engine will bring up some others.