Validating Windows here, again.

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.

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.