You might try this. It worked for me and many others.
Re-register the Windows Update DLL with the commands below
Click Start, click Run, type cmd, and then click OK.
Type the following commands. Press ENTER after each command. Wait for succeeded after each entry before proceding to the next entry.
regsvr32 wuapi.dll
regsvr32 wuaueng.dll
regsvr32 wuaueng1.dll
regsvr32 wucltui.dll
regsvr32 wups.dll
regsvr32 wups2.dll
regsvr32 wuweb.dll
Attempt to run Windows Update
Also try the Windows Installer link for Non-Vista machines from Microsoft.
http://support.microsoft.com/kb/315346