go to http://www.amazon.com and buy the NXT 2.0 discovery book. You will find instructions for the snatcher and a game program! I'm sure it will help your constant building!
One model only needs two motors, one cable and four wheels. They are the main parts.
1. Attach two wheels to the front of one motor with a 7m axle.
2. Make the back wheels by attaching them to the last hole in the side of the motor. Use a 12m axle to attach.
3. Push the cable into both motors and turn the motor with nothing on it. The car moves!