Check this little drive out:http://robokitsworld.com/index.php?main_page=product_info&products_id=15&zenid=896tikqhfgd15i5b4l6jvpclb5
Very inexpensive (I havent checked shipping yet, sometimes they grab you by the family jewels there).
It can control one or two motors.
Make sure the motor you want to control doesnt draw over 5 amps before you order it.
If the motor you are controlling only draws an amp or two you can check out the secret drive others on here are using (Not sure about the current capacity on it.)
Yes, multiple motor control is very possible using USB.
Just buy multiple USB IO boards if you run out of IO for your motor drives.
You could theoretically control up to 4 motors with the printer port. But you only have 5 inputs, so that could limit you to two motors, if you use limit switches that feed back to the PC.
Mrotate3 can control multiple motors from the printer port and it can do it very simple.
For instance, if you wanted to control two motors, download two copies of MRotate3.
Place them in different folders.
Name the folders "MRotate3" and "MRotate3A"
Assign each executable it's printer port pins that control it's motors drive. (The pins would have to be different for each MRotate3.exe)
Set each motor's properties (speed, time limits, etc) through its copy of MRotate3.exe (Using MRSetup.exe in the same folder as that Mrotate3.exe)
Then have your software call MRotate3.exe in folder "MRotate3" for motor #1 and the one in folder "MRotate3A" for motor #2.
They only problem you might have is trying to run both motors at once. Two copies of MRotate3 running at the same time would argue with each other over control of the port.
If there is a big enough desire to do this, I can modify MRotate3 to control multiple motors with just one exe.
Good luck on your project and keep us informed. Let me know if you need help hooking up a drive to the printer port.
You may also want to check out the beginner's guide thread in this forum.
EDIT: I reread your previous post and your motor does draw 5 amps, so the drive in this post should work, but I think I would install heat sinks on the transistors cause you will be pushing the limits of that drive, especially if you plan to use PWM for speed control. Let me know if you need more info on the heat sinks. Or you may just want to buy a bigger drive.