I highly recommend that site mentioned above btw for any robot fans... David Cooks book I think was seriously one of the best Ive read (for a newcomer like myself) into all aspects of robotics, plus as you can see, he knows a thing or two about electronics too.
Actually the windshield wiper motor spins like any other motor. It uses an arm with a ball on the end and some other linkage to move the wipers back and forth.