I have used the dry ice method for removing dents before. It actually does work pretty good. I had a dent from a foul ball at a little league game. I wrote an article on how to do this on DryIceNetwork.com. Basically here are the steps of what I did:
Heat the area with a hairdryer
Apply dry ice to center of the dent
Remove dry ice and allow it to warm up
Repeat 3 or 4 times if necessary