Procedure to manually Re-Install Automatic Update Client
Go to the Windows Command prompt (CMD.EXE).
From the CMD.EXE prompt, run the following command;
For Windows 2000 SP4/ Windows 2003/ XP RTM and SP1
rundll32.exe setupapi,InstallHinfSection AutoUpdate 132 %systemroot%\inf\au.inf
After running this command, you must restart your computer.
Once restarted, you can open the Services Control Panel Applet and check to ensure the Automatic Update Service is installed.