jake i know there's a map someone made out there to test this where you could drive the tanks, jeeps and trucks. saddly i don't remember the name of the map but it obviously can be done.
ya, there were 2 of them i know of, one was called jeep tank test or something like that, and the other one was the secret m4l0 level, but with a bunch of dogs, useable flak88's, and a few tanks that you were soposed to be able to use. but the problem is that i couldnt get in them 99% of the time!