This page should give you some ideas (not mine):
**broken link removed**
Note that you should only do the diode thing with the limit switches if they are designed to handle the current/voltage loads of the motor. But basically, if they can, then you can use a 3-position (On-Off-On) return-to-center DPDT switch (where center is off), cross-wired an h-bridge config (make sure the switch is rated for the current capability of the motor) to control the whole thing. Also - install a fuse (rated for the stall current of the motor) just after the positive battery connection to this setup (unless you want a wire harness fire at some point in the future).