Automatic Update Service Causes "Blue Screen"

My question involves WinXP Home w/SP2 installed. I'm trying to help a friend
with his computer. After much spyware, adware, and virus scanning, his
computer still shuts down to the infamous "blue screen" UNLESS Windows
Automatic Update Service is unchecked in "Services" using msconfig.

If I start Windows with the Automatic Update Service turned off, then turn
it on manually, the computer will "blue screen" in short order.

I have tried reinstalling SP2 from a MS CD, but the problem persists.

Is there a way to do a "repair install" of WinXP Home? Is that likely to
solve this problem? Obviously, I'm trying REALLY hard to avoid a complete
reformat at this time.

Thanks to any and all for your help.
--
JLarsson