Houston we have a problem.
The roborealm allows direct control to the SERIAL PORT and NOT the USB port.
Once you figure how to directly control the USB port from a program on your computer, then look at page 8 of the user manual http://www.pololu.com/products/pololu/0101/smc01a_user_guide.pdf
for the syntax of the serial commands.
On the website it says
The USB adapter's drivers make it look like a standard serial port to the operating system, allowing you to connect to all of your existing software, such as servo controller interface programs, through a USB port.
If what the website says is true then you would just select the virtual serial port. Tell me what happens,( install all the drivers from the roborealm website)
read the user manual a bunch of times, and remember to look at circuits using that motor controller, and figure out the voltages and amperage needed to NOT fry the USB port/ serial port.
More details about the virtual serial port or if its just a USB port!