Pasadena, from all the other great posts I thought you would know this one!
Torch shrinking is most definatly something you'll want to practice before attempting it on a sweet peice of sheet metal. The basic idea of it is to heat the steel and cool it at a faster rate causing the steel particles to "shrink". Now in doing this some people use blocks of ice, frozen rags most anything cold will work. You just have to learn to use it. Now the torch part is the tricky part. Heating the metal at the precise spot of convexion is the key. Of course this will heat the rest of the steel as well so when cooling you have to pinpoint the spot you want to shrink and only that spot or you could very well have a huge disaster. Now, find the stretched spot of steel and only do one at a time, starting with the biggest first. Pinpont that spot with the hottest part of the flame untill the spot becomes red glowing hot. Be [B]VERY[B/] careful not to burn through the steel, its very easy to do. Now when the spot is glowing the particle are spread farthest apart, by introducing something cold the particles with naturally "shrink" back together, depenedant upon the rate of cooling, the faster you cool, the more it will shrink, the slower it cools the less it will shrink. So of course by pinpointing the rate of cooling you reduce the chance of shrinking the metal inadvertantly around the spot your trying to shrink. Practice before you use it, its pretty tricky. Of course you could just result to a claw hammer and shrink the metal with two wacks, but thats just to easy for me.
I've seen guys heat a spot and use this giant rag and bucket and slop icewater on it to cool it. Let just say it wasn't pretty <img src="graemlins/drunk.gif" border="0" alt="[drunk]" />
Also for those of you with ready access to dry ice its a wonderful dent remover
HK