No help here but I feel your pain. I have Acer laptop with Home Premium 64-bit. Here is my experience:
I have kept my laptop updated but decided to give the sp1 a go. Sorry I did. My download was interrupted the first time I started. Now whenever I try to start again it sits at 0% and my hard drive light stays on constantly. I left it go that way for half an hour but was afraid I was going to fry my hard drive. Managed to do a restore and everything back to normal.
I would advise against this if you've kept your system updated.
Well, I finally got it to work after deleting the files in \Windows\SoftwareDistribution folder. Still took over 2 hours on a laptop that had all the current updates. Long periods where it appeared it had stalled or locked up with constant hard drive light.
Not a pretty install and sad that the user has to take unusual actions to make it work.