[Al Skierkiewicz]

Dave,
I am going to make the assumption that this application is NOT a FIRST robot since what you are asking to do does not fit exactly the rulebook. That being said, remember that a falling weight, slowing to a stop will have a varying input to the motor and thus a varying output current. Even a fully shorted motor will still be able to move so a mechanical brake will have to be employed as well. The choice of motor will depend on the weight and pulley design but it would seem that the drill motor with transmission ought to do a nice job for weights under say 10 lb. (You will have to experiment with motor depending on the weight and length of travel. i.e.the chippy seems to high an RPM to be effective for small weights over short distances.) You will be back driving the transmission so the motor load would be able to allow more finite control. As to producing the variable resistance, some form of feedback will be needed such as a tachometer on one of the pulleys. Integrate the output of the tach so you have some reference voltage, feed that to a simple multistage window comparator. Use the output of the comparator to switch in fixed resistors in parallel with the motor. Add an end of travel switch to click in the mechanical brake and you are done. For more sophistication use the output of the tach for speed and distance reference and servo the loop to the resistors and brake. A Basic stamp would work nicely I think.
True it's not like riding a bike but you know this stuff. You just have to remember where you put the info in the garage of your mind. A little search and you will find the right box. The downside is the other stuff you are going to find in the mean time. (No comments Joe!)