You definitely want more RAM. 256 is barely enough for Windows XP to run, let alone play games with lots of textures to swap back and forth.
The mouse problem may be a controller conflict in AH. Check to see that your joystick and related equipment is setup as your controller for the various functions, not the mouse.
Moving to gunner positions, use the number keys above your keyboard. 1 is driver, 2 through (i think 7 is the highest number any vehicle uses, that would be the PT boat) are the gunner positions.
And from one former AW'er to another, welcome.