I’m working on an HP pc with the stock NVIDIA 8400 GS video card.  On 9/5/2009 Microsoft Automatic Update installed a Microsoft Silverlight update (KB970363) that stops the NVIDIA video driver from loading.  I’ve gone back to System Restore before that update twice to see if it’s something else and the Silverlight update is the one that breaks me.  It’s shown as an “important update” so Automatic Update will continually attempt to reinstall it.  It looks like my only option is to uninstall Silverlight.