I can't guarantee an answer but try doing a disk cleanup to clear out the old update files (my computer, right click C:, properties, disk cleanup), then look for and delete a folder called windowsupdate in Program Files, reboot and try again. I take it you are logged in with an administrators account? If the updates can be downloaded but not installed, as a bodge you could try using this click here to store the files for manual installion. Not a fix, but one way round it. Also, a diskscan with chkdsk /f at the command prompt would reveal any problems with your hard drive that might prevent files being saved properly.