Would someone verify I am looking at this correctly? It looks like either could handle the green motors, but not the yellow motors unless you prevent the motors from stalling.http://www.robotshop.com/dfrobot-4wd-arduino-mobile-platform-4.html
Indicates a stall current of 470mA @ 6 volts for the green motor and 2.8A @ 6 volts for the yellow motor.
The chassis appears to use 4 motors, so if your driver is 2 port, you would need to double the stall currents as you would have 2 motors on each port.http://www.adafruit.com/products/81
provides 4 channels of 0.6A continuous capacity (each sufficient for the stall current of the green motors)http://www.amazon.com/DFRobot-Motor-Shield-for-Arduino/dp/B006D85PAS/ref=sr_1_4?s=electronics&ie=UTF8&qid=1323643740&sr=1-4
provides 2 channels of 2.0A continuous capacity (each sufficient for the stall current of 2x green motors)