Soundproofing Question

Does anybody have any advice on soundproofing a car? I'm figuring that most of the sound comes in through the doors and the wheel wells, but that is just a guess. If anybody has any suggestions on what materials to use and where to put them, that would be great.

The other thing I have thought about would be to use the stuff they use to coat the beds of pick-up trucks. Would this stuff work? I know it would be easy to apply to all of the spots on my trunk. Or how about asphalt roofing materials? Would dynamat be the only way to go?

-Thanks

(sorry, have had the urge to use this for a while, this is as good of an excuse as any :-) The big recent discussion on this is here.

Ow!!!

Funny, though...

I actually had read that post. Look at the bottom of page 2, I even posted a message there prior to this one. So, maybe I should of asked this question at the end of that one. But, I thought this was a little different.