I thought I'd add in a couple comments on some of the older posts...
First, the motors. The 12' x 7' x 35' measurement is really the measurement for the entire motor *assembly* at the top of each drop shaft. The electric motor itself is about 3'-4' in diameter, and a few feet deep. In the overall assembly, it's actually rather small compared to the rest of it. The motor is on one end. There is then an axle that runs from the motor through what amounts to two huge drums that the cables wrap around (with brakes and stuff within the shells around the drums). I'm 99% sure the motor drives the axle directly, there's no transmission involved.
One of the cable drums is centered over the shaft, the other is above one of the side walls. From the centered drum, a cable runs down to the VVC (the "cage" that the ride vehicle rolls into in the shaft). From the other drum, a cable runs down the side of the shaft to a large counterweight that travels up and down the side of the shaft, opposite to the VVC. (When the VVC's at the bottom, the counterweight's at the top). There's a third cable that runs from the bottom of the counterweight down through pulleys at the bottom of the shaft and back up to the bottom of the VVC. There's tenstion on all cables all the time. Thus, as the motor turns in either direction, it's actually driving the car up and down the shaft. The limit to how fast the car can go is really a factor of how fast the motor can spin as well as the wind resistance of the car working against the motor.
I have a friend who took a video camera into some of the backstage areas of Tower during his last week on the CP. Even up onto the catwalk behind the HTH sign out front with his manager's blessing (and accompaniment). He set the camera down on the catwalk and walked away while it filmed a cycle or two. One of the shots was up in the motor room with the motor going through one entire cycle of Tower version 2 or 3... I'll have to see if I can find it.
-Rob