I doubt the above is the case since otherwise Vista probably wouldn't have installed correctly to start with.
First off I'd recommend downloading it again, it's not unknown for corrupt downloads to cause this sort of a problem. Failing that:
It's possible there's a driver conflicting with it - try disabling devices one at a time and see if that helps. You might also want to run scandisk to check for any disk surface errors (these may well throw the installer off.) It's also worth running memtest just in case it's a memory issue - again that could cause a sudden deadlock.
If all that fails, you could try making an image of your disk, wiping it and restoring it to factory settings, and then putting the service pack on then. If it goes on then you know it's a software conflict somewhere down the line, if it doesn't then it's something deeper - perhaps contact microsoft, check for any existing issues online with other users and wait to see if a fix is brought out that works for you.