Pic up a BOE from Parallax- that will be you onboard processor. Video... you'll need a whole seperate system for that. Use 4 of the 7.2v cordless drills on
www.harborfreight.com for drive- you'll need to either use relays to control them via the BOE(off/on), or you can figure out a way to do PWM control with hobby ESCs (proportional). For the arm, you can use 1/4 scale servos from
www.servocity.com, and some normal sized ones for the claw. Get your NiCads (7.2v-8.4v) from
www.towerhobbies.com and a decent peak charger.
If you want to actually conrol it from the PC- that's a whole different can of worms. Forget the BOE and get a hobby radio control system. Trying to control it with keyboard and mouse would be very complicated the RC would be easier than the BOE (less wiring) and interfaces with PWM directly, so you don't need any middleman to the hobby controllers or servos. You can just sit at your computer and use the RC controller.