Windows XP Professional allows you to turn off auto restart aspect used by Automatic Updates. Many times after you do inform that needs a restart Windows will restart PC for you devoid of you knowing it if you are not sitting opposite it. This is not a good thing to perform if you have something operating on PC that you have not saved or cannot be closed.
To modify this setting you can use Windows Group Policy Editor by following these instructions:
1. Go to Start, Run, type gpedit.msc, click Ok.
2. Go to Computer Configuration\Administrative Template\Windows Components\Windows Update folder.
3. Double tick No auto-restart for planned Automatic Updates systems. In dialog box that shows, choose Enabled and then tick Ok.
4. Close Group Policy Editor window.