I believe the air solenoids are operated by 24v DC so if you can find a suitable sized 24v DC motor you should be able to disconnect the wiring to the air solenoid and reconnect it to your motor. Should be a reasonably easy modification.
My machine's alright, well kind of anyway, it missed a load of steps the other day have a look here
http://cnczone.com/forums/showthread.php?t=62706
Here's the pegs I've been making.
Cheers
Chris