How to flush the Windows Update download cache

If Windows Update ever fails to install an update, one possibility is that the download was corrupted.

To flush the download cache for Windows Update, follow these steps:

- Stop the Automatic Updates service ("services.msc" at the "run" prompt
- Browse to the "SoftwareDistribution" directory in the windir ("%windir%\SoftwareDistribution" at the run prompt)
- Delete everything in the "Download" directory
- Restart the Automatic Updates service

That should do it. Try Windows Update again. You can confirm that it was successful by noticing that Windows Update downloads the patch in question.

On a related note, updates to some Microsoft products (Silverlight, .NET, etc) may not install. One common way to try to fix that is to uninstall the offending product and reinstall it. Sometimes, that product will not uninstall. This little utillity from MS will let you forceable remove MS products. Great for when the uninstaller gives you the finger.
http://support.microsoft.com/kb/290301

Thanks to:
http://www.troublefixers.com/how-to-remove-downloaded-but-not-yet-instal...
http://l370.blogspot.com/2007/02/clearing-windows-update-cache-upon.html