Dunno 'bout Vista but in XP you can set your update preferences to download but NOT install unless/until you want to. Which is what I have done. Of course you must be careful how you shut down your computer then because doing it the regular way will automatically install all downloaded updates. To avoid this you must click on a small text line on your shut down screen, NOT on the big "Shut down" button.  If you forget -- and I did forget one night when I was too tired to think -- you could end up with unwelcome surprises when you next reboot. A security update for Internet Explorer got accidentally installed; luckily it only broke Word Perfect, I didn't lose anything else. Still annoying as hell, though.

Which is why I have no plans at all to install the latest XP patch. Merlin only knows what that'll screw up!