First download the WGA update executable »www.download.windowsupdate.com/m···49a0.exe
Put it into c:\temp\ folder.
Rename it "a.exe" just to cut down on typing.
Download psexec which you can get from here:
»www.sysinternals.com/Utilities/PsExec.html
Put that into c:\temp\ folder also.
From the command prompt enter:
c:\temp\psexec -i -s c:\temp\a.exe