You have 4 choices on Autoupdates:

1. Automatic: Downloads, Installs and Reboots
2. Download Updates for me, but let me choose when to install them.
3. Notify me but don't Automatically download or install updates.
4. Turn Off Automatic Updates
   And there is a time in the beginning when you are prompted after an Autoupdate, download,
   and install to reboot and if you check the little box to remember to reboot everytime then that 
   is why Windows reboots. Don't check "Remember this setting". For now take Option 4 and wait about a week then do a manual Update and Don't check the box when it prompts to reboot. 
   @ Paula, Sorry we don't have Vista up here at work yet for me to work on, so I am unfamilier with it's intricate settings, but there should be some Deep Rooted Setting to fix that. Have you been to the Autoupdates Overview Folder found in  Control Panel/Autoupdates/How Does Autoupdates Work?

I would rather be Politically Incorrect,
Then have Politically Correct-Incorrectness!!!