Microsoft Vista Service Pack 1 RC - Installation Nightmare!!!

I downloaded the service pack from MSDN this morning and kicked off the installation around 11am. It is now 3.15pm and it is still installing...

I think the installation has gone bad. I can tell because for the past 4 hours or so, it has been rebooting my notebook repeatedly. The sequence is

1. Vista starts
2. I see "Please wait..." message and then "Configuring updates..." message
3. Shutting down...
4. Step 1

When I ran the single executable, it said "it will take about one hour" but 4 hours? I am not sure how to stop this! I tried pressing F8 during boot and tried Safe mode etc. No luck yet!

Microsoft, please help!