General information

Learn how to install Windows Vista Service Pack 1 (SP1)

Unlimited installation and compatibility support for Windows Vista Service Pack 1 (All Languages) is available at no charge until March 18, 2009.

Does not boot after SP1 installation

Try to boot in safe mode. If this works, the most likely cause is a driver problem.

Try to identify the problem driver and install a working driver in safe mode.

If all else fails, uninstall SP1

Instructions: How to uninstall Windows Vista SP1 as a troubleshooting step