Pretty good game
I liked this game a lot. It shows a lot of effort.
One thing you might want to consider: even on low quality it got slow in the parking lot when a lot of action took place (i have a p3 1GHz with lots of Ram). Try to reduce the use of gradients. Another thing you could try: use a .gif image for the backgrounds. Why? I am currently making a sniper game and when I replaced the background with a gif image, the processing got a significantly faster. That might do the trick. I'm not sure if 4 players could really play this game - or even 2. I played a computer car racing game with my brother (both using keyboard) and when we pressed 4 keys simultaneously, all controls locked. I'm not sure about newer keyboards though.
Finally, I liked the AI in the game. Keep up the good work
Istvan_from_TutiTV