If your Vista/7/2008 machine gets stuck installing/configuring update 3 of 3 after a recent update cycle, you can follow this procedure, but ONLY as a last resort. BEWARE: this may leave your machine in an unstable state. to read about why this occurs, check the following link: The Windows Servicing Guy

1. Boot to safe mode, if at all possible.
2. Click on Start
3. Find the command prompt in the start menu and right click on it
4. Choose “Run as administrator”
5. Type takeown /f C:\Windows\winsxs\pending.xml
6. Type cacls C:\Windows\winsxs\pending.xml /G :F
7. Type ren C:\Windows\winsxs\pending.xml