I just came across this really interesting instructable about controlling motors with the Arduino. It looks like a really simple, and cheap, way to use an L293D chip for use in robotics. Check out the link for all the details and code.
After long research and trial and error, I have came up to a new walkthrough regarding this nice chip, the L293D.Each project is one project and each one has its own unique power configurations, so you must be aware of the best battery choice and how to distribute voltage through your robot.
In the Maker Shed: