This is possible, but you would need still need a few major items:
- An IO board. See below for more.
- Speed controllers, relays, etc. Victors and Jaguars work well from any device which can drive hobby servos.
- Code to control all this. This is largely dependant on the IO device you use.
- Any hardware, motors, etc.
I've used the following for IO boards.
- Phidgets(http://phidgets.com). Easy to interface with, but you would probably need 2-3 boards to build an interesting robot. $100+
- Arduino(http://www.arduino.cc). Inexpensive, with lots of IO options, but not designed to be an IO board. Lots of custom code would be needed. $30+