XP Pro, SP3, heavily updated, T42 Thinkpad

I have an update that won't update. That is, new Microsoft update
proceedures give me a "Failed to install" message on it.

As bad or worse, it will not remove (Control Panel Add-Remove) either.
After telling me that some previous installation archive can't be found it
ultimately gives me a message that vs_setup.msi cannot be opened.

(It seems possible or probable that this problem is at the root of a recent
triple undate failure.)

I googled this literally for hours and discovered that everything about
vs_setup.msi is complicated, tricky, esoteric and probably insolvable short
of a 5 genius attack or total reinstallation of XP.

But I'd be glad to hear of an easy explanation/fix.

Thanks

--
JimL