Hija Gyro!
First of all, you need to set up that mouse of yours

. Check
THIS THREAD for a PDF on how to go about it. Make sure you have Mode2 mapped (thats the ground vehicle (GV) mode).
To drive a GV. Make sure youre in mode2 (either check the box in setup to switch modes automatically or assign keys in your Key Map Setup for Mode selection). Start engine with E. Switch into first gear with Q (Q gear up, W gear down). Then move your mouse away from you to accellerate. Mouse left and right to steer. Mouse back to brake.
Numbers key to switch to the gunner positions. 1 for drivers seat, 2 - 6 for guns as available. You can steer your GV while in gun position by using the RUDDER (A and D keys, S to center).
To launche the torpedoes on a PT boat, you need to open that launch bay first with O key.
Check out
Hammer's Net Aces for a onepage Quick reference to Default Keymap. Print that out and have it handy on your desk. Makes thing a *lot* easier at the beginning (heck, after two years I STILL have that thing next to me when playing

)
Hope that helps

.