Updating iPhone 3G.. Failure. Help?

Alright, I started to update my iPhone 3G and iPod to 4.2. Everything was going smoothly, and then my iPhone's bar below the apple stopped at the very end (probably about 5% remaining) and stuck there. I updated it on another computer and it worked fine.. Can someone tell me what's going on? I'd hate for something to be going wrong on my MacBook Pro

I had this same issue.
The IPSW file got a little corruption in it when I downloaded it and so it wouldn't finish loading on my MacBook.
I called a genius and they suggested I delete and re-download the file and that worked fine