Windows Update Forum:
This is the Vista Install, Upgrade and Activate Forum.
You will get the best help for any Update/Service Pack problem in the Windows Update Forum; link below:
http://social.answers.microsoft.com/Forums/en-US/vistawu/threads
When you repost there, kindly include any Error Codes, and exactly what happens when you attempt to Update.
That way you will receive the best help there.
Cheers.
Mick Murphy - Microsoft Partner