Adding on here:
Once you have a continuous rotation servo, in case you need an example of using the API to drive servos in one direction or the other, here is some code for a car that just drives forward. It uses two servos, one going "forward" and the other "backward". Forward is ~move(servo, 1); backward is move(servo, 0).
If you want to go the route of hooking up motors, this tutorial might help.