It is a riddle, wrapped in a mystery, inside an enigmaSorry, I know that's not helpful, but whenever I see .Net ANYTHING...my usual response in
A) NONE (Better to remain silent and be thought a fool than to...you know the rest.
or
B) RUN. RUN FAR. RUN FAST.
Having said that the least I felt I could do is provide a link to the KB in question, at least it provides you with a starting point. The link:
http://support.microsoft.com/kb/951847Read through the article and try to determine what might be preventing the update from installing. Perhaps you might want to download the update executable to your hard drive and try to install it that way instead of through WinDOZE Updates? The KB I linked you to provides links to the appropriate .exe download pages with detailed instructions on how to install, PRECISE order you should install each .exe, etc.
I'm no expert, so please proceed with the utmost caution before acting and if you do PLEASE backup your registry & create a restore point beforehand.
I hope this helps a little.