Automatic Updates
Short name wuauserv
Related file(s) wuauserv.dll
Default setting Automatic
Log On Account Local System
Depends on None
Services that depend on this service None
REG file wuauserv.reg
Image path %systemroot%\system32\svchost.exe -k netsvcs
Registry location HKLM\SYSTEM\CurrentControlSet\Services\wuauserv
Description This service enables the download and installation of security updates for Windows and Office automatically. If this service is stopped, updates will not be automatically downloaded to the computer automatically. You will need to download the updates from Windows Update Web site.
Comments Automatic updates setting can be configured via Start -> Control Panel -> Security Center -> Automatic Updates

More details at this URL:
How to configure and use Automatic Updates in Windows XP