I used to have this old Saab, which was the perfect vehicle to take to SukMart...didn't matter if anyone tagged it, ran great, rode great, 186K when I gave it to my buddy.
It had a few big dings on it from pigs that swung the door open on their 1976 Bulgemobile and didn't give a **** what was in the way, as long as they could rush right in there for their next cartful of Twinkies. A guy at work told me about something similar to the link I'm posting below...he suggested I turn a spray bomb of compressed air (like to clean keyboards) upside down so it came out as a super-cold liquid I'd then spray on the dent, wait a minute or so, then heat the area with a hair dryer.
I tried it and it didn't do a dang thing.
So I did it again, and this time used a heat gun that I have for stripping paint and applying shrinkwrap. Hey, it was a 14 year old car with a zillion miles on it...who cares, right?
Maybe a little bit came out...I'm not sure...but I am kind of an optimist. I never thought about using dry ice like this guy did. Apply at your own risk!
I was trying to find a video with the aerosol can, but saw this instead:
Rather than take the door apart, you may want to invest in a slide hammer...use some hobby-type hot glue to glue a heavy suction cup over the dent, hook the tool to the suction cup and work the slide sharply a couple times...won't be perfect, but it should pull biggest part the dent out. The hot glue should come right off your paint without damage (assuming there are no chips you'll make "run" by picking off the glue with a plastic razorblade.)
Then you can get Grissom and the CSI team to track down the culprit and re-dent your door...with his forehead...