I've made a GTA car physics example, it uses the Physics Plugin.
After many hours of work, I finally got a decent top-down car simulation (without wheels, just one object but many events).
If you think it can be tweaked and improved for a more realistic simulation, post here your caps with the modified configuration.
I know I could've easily added acceleration variables and things like this, but I don't need them so it's up to you if you need them.
Here's the cap: http://dl.getdropbox.com/u/1105488/GTA_car_physics.cap
Make a good use of this!
p.s.: I used 98.9.