I *think* Op. Wolf had 2 different possible types of gun: optical and positional. If it is the positional type, then you can interface it like an analog joystick as it will use pots. If it is optical, you can't interface it atm.
The above statement could be wrong, it might have just come with positional guns. Either way, positional guns should work (people here have done it), although it might be hard to calibrate the gun's physical position with the on-screen target.
Also, do a search on this board, the subject has come up numerous times
