Turn automatic updating on or off Applies to all editions of Windows Vista.
To have Windows install important updates as they become available, turn on automatic updating. Important updates provide significant benefits, such as improved security and reliability. You can also set Windows to automatically install recommended updates, which can address non-critical problems and help enhance your computing experience. Optional updates are not downloaded or installed automatically.
1. Open Windows Update by clicking the
Start button

, clicking
All Programs, and then clicking
Windows Update.
2. In the left pane, click
Change settings.
3. Choose the option that you want.
4. Under
Recommended updates, select the
Include recommended updates when downloading, installing, or notifying me about updates check box, and then click
OK.

, If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
Source: Microsoft