I just played one race, and this seems to be one of the better racing games for the DS (not that that's saying much). Graphics are pretty good for the DS as well.
Car-fu: You press (B) when the icon shows up over a car that's in front of you to jump. A bar shows up at the top of the screen with two icons heading towards the center. You press the button indicated when your icon is over the center box to land on your opponent, thus ruining their day.
You can also do a spin attack. This will also right your car when you can't get it pointed in the direction you're headed in.