Also it doesn't seem to be able to control the direction of motor rotation.
Relay H-bridge (buy more parts.)http://forum.arduino.cc/index.php?topic=79431.0
Presumably the board supplies the 5v to the pot, and reads back the value of the middle pin.... So, it "might" be feasible to put the Arduino ground pin to the Control 0v and then to PWM the Control "INP" pin from the Arduino, which will give it a "pseudo-voltage" between 0 and 5 for speed.
I'm not sure JimboZA.
I can't read that 8-pin IC, though.
If it needs a true variable DC, PWM could be smoothed out (buy more parts.)