First up, good work. Nice and polished. Let me give my likes and dislikes, and I hope they help.
Likes:
-Ran smooth on my system P2200, 1GB RAM, GeforceFX 5600 128MB, but what do you expect?!?
-Models and look generally looks pretty good. Overall, nicely designed, especially the car models.
-Played pretty well, and I didnt have any problems with crashing or slow down or anything.
-A.I opponents were fairly convincing (i.e. they didn't look wrong, and they were about the right level of difficulty)
Dislikes:
-Physics is hard to do well, so I appreciate it's not an easy task. However, it wasn't too great. By all means keep it as it is, but I think the cars need to slide a bit, and not slow down so much when you turn tightly. Seemed a bit sudden. The fish tailing rear end of the car was a bit OTT. I'm guessing it was an animation. Wasn't too bad though.
-Collisions are a bit annoying. Once again, I know it's hard to code bouncing collision and momentum transfering etc. but it's not fun stopping dead each time you collide with something.
-Music was a bit low quality, but I'm guessing you did that to reduce download size, so fair play.
-Car sound FX were too quiet. Had the same problem with the other racer here.
So overall mate, good work. Nice and polished and finished, but would be more fun with slightly better physics and collision. Anyway, nice job.
Insiiiiiiiiiiiiiiiiiiiiiiiide!