Help with "Night of the Living Dead" Mac.

First off I know nothing about macs. My neighbor needed help installing AOL on his laptop and I offered before I knew he was using a MAC. Had I known what I was getting myself into I would have pretended I was not at home when he came knocking at the door. ;)

Here is the problem: We can't get the blasted computer to shut down! It's completely frozen, the restart button will not work. We have unplugged it from the wall. The one thing that is working beautifully is the battery!

Any other way to shut it down short of waiting for the battery to die (or taking a hammer to it?)