The BACKSPACE key is the default key for cycling secondary weapons. Use it to switch to bombs or rockets, then hit B (or your secondary fire key on joystick/mouse) to fire.
You might take a look at
http://trainers.hitechcreations.com Most of the basics are explaine there, for example not only how to drop bombs, but also how to HIT with them
And yes, you can fire the jeeps MG. Hit number keys on keyboard to jump between driver & gunners position, just like you do it in tanks.
