From: "Frank Haber" 

This is hitting the fan in several places (Channel 9; Old New Thing, etc.).
People have been bit, and they're not happy.  Me, I got an autoupdate
failure, apparently mercifully.  But when I uninstalled a progam and went
to reboot for other reasons, there was a peculiar new option in my
(Classic, 2k-style) shutdown dialog - "Reboot to install
update(s)!"  Poor show.  Any reboot dialog had expired or vanished
while under other windows.

It seems you can fiddle with gpedit to turn off auto-reboot, but only if
you set an update schedule.

And there are reg entries to do it with an axe...

http://www.microsoft.com/technet/prodtechnol/winxppro/maintain/sp2maint.mspx

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