In C: \windows\system32 the following files appear to be involved with updates
wuapi.dll
wuapp.exe
wuauclt.exe
wuaueng.dll
wucltux.dll
Although those are W7 file names I suspect Vista may well be the same. If you have another Vista MC you could try copying the files across having first renamed the existing ones using the word old at the beginning so that you can restore them if need be.
PS you'll need to enable 'show hidden files and folders' option.