Many people want to know how to get the 360 car. The truth is you can only get it and other cars such as the Alienware, Yellowcard, and the Spike TV car through Xbox Live. So if you want it you have to pay to get the service, which is a nice $50 a year.
On Xbox Live the best two cars are the Nixon Special and the Revenge Racer. The Nixon is good because it is light, nimble, takes off fast, is good at dodging traffic, and is very good for beginners. After you've tried the Nixon use the Revenge Racer It has the higest top speed for some reason. All other cars have 209 max top speed, but the Revenge Racer has 212 giving you a slight edge over the competition. I should know because I'm ranked 1743.