Are you running Windows Live OneCare? That's the topic of this forum -
http://onecare.live.com OneCare does advise you if important updates fail to install, so if you are using OneCare, you can contact OneCare support -
How to reach support - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
If it fails to validate your subscription, select the option that you are using a trial or beta copy and you can proceed to email support without validation once you've signed in.
If you are not running OneCare, you may want to check out the Windows Update Solution Center for help - http://support.microsoft.com/default.aspx?PR=wupd
-steve