BleepingComputer.com: Vista stuck in update loop, I don't have Product key to start from scratch

My laptop fell into a never-ending cycle during a Windows Update. When I turn it on, it boots up fine, then goes to a "Installing Update 3 of 3..." page, from which it eventually restarts the computer, only to do it again. I've tried the repair option, safe mode, etc, etc, and I've searched forums all over with no working solution. I can format the hard drive if needed, but as a laptop, it didn't come with a installation disk, and the sticker on my laptop has long worn off the Product Key. I know that if Vista's running I could retrieve this key and I know how I would format the hard drive if Vista was running, but it's not. A couple of thoughts/questions, responses to any of which would be much appreciated.

Is there a way to boot to the command prompt?

If so, how would I go about recovery?
Is there a way to retrieve the product key from the command prompt?
I restored the system last year from a partition on the hard drive--is there a way I could access this from the command prompt?

Thanks in advance... I'm stuck without assistance...