Stopping Windows Update Auto Reboot
How to prevent Windows from rebooting after automatic updates
By default Windows is configured to automatically download and install updates. This is fine, as it saves you the trouble of checking for updates and installing them periodically. But the problem is that, once the updates are installed, Windows needs to reboot. Windows usually sets itself to reboot in 10 mins, but it also gives you the option to postpone it. So, if you are working on something important, you can postpone the reboot.
But, what if you have some important and  unsaved work in progress and you have to leave your computer for a little while, and right at that moment, Windows installed some updates and rebooted itself. The result, you lose all the in-progress work.

Here is a simple and easy fix to avoid the above annoyance.

1. In Vista or Windows 7, click Start, type Windows Update, and hit Enter. In XP, open the Control Panel and select Automatic Update from the menu of options.

2. In Vista/Windows 7, click the Changes Settings option at left. In XP, you can simply skip to step 3.

3. In Vista/Windows 7, Change the setting to Download updates but let me choose whether to install them. In XP, change the setting to Download updates for me, but let me choose when to install them.

4. Click OK.

That’s it. From now on, Windows won’t reboot without your permission, though it may still nag you about installing the downloaded updates.