Well guys, thanks for all of the suggestions. Although I'm not a cat lover I'm not really interested in killing the cat, so the poison /.22 is out. I may look at the airsoft, and the ultrasonic noise maker. I've also done some researching and found that most cats don't like citronella or pepper spray so I could just try spraying some of that around the car and see if that helps.
I just think it's really wrong headed and inconsiderate that someone will not keep their pets in the house. I mean seriously, if my dogs start barking I bring them in. I don't let them shit on someone else's lawn...
As far as talking to the neighbor, if that goes badly and something does happen to the cat, then I'm #1 on the 'shitlist'. Damn them for putting me in this position.
Josh