Update: I'm not sure where I saw the "square drive" I was talking about...there is not a square drive on the motor, it's just a regular toothed gear that's about 3-4" in diameter (the diameter of the round part of the motor).
I actually had two problems. The motor failed at some point and when the window fell down in the track it apparently damaged some plastic parts on the regulator. When I pulled it apart to inspect I saw the obvious damage on the regulator and assumed that was the only issue.
Also, here's some good info on testing these items...i.e. motor, amp, switch
http://www.nicoclub.com/FSM/240sx/1989-90/POWER_WI.pdf