Yeah, I have a Vista machine and an XP machine. They both run well, but they are configured to regularly update and I don't have internet at home. So when I take on out to a wifi coffeeshop it'll automatically absorb the latest updates from the Windows mothership and it regularly attempts to do an operating system update. It does not usually ask for permission, and it does a shutdown/ restart on me as well.

If like me you do not regularly update you can get in a position where it does not do the updates in order, and this can cause problems. You should do like EBarnacle suggests but pay attention to whether or not it has 'missed' an intermediate update. This could have caused a hiccup.

You can also email microsoft for help, or my favorite volunteer online help site: www.techguy.com.

Hope some of this helps.