Here's a URL to an old web page that has some good info on how to use the Roomba R2 printed circuit board H bridges to control motors using a PWM signal from your favorite micro-controller.http://www.dinofab.com/roombahack.html
The web page left me with a couple of questions so I hooked up the EZ-B controller to see what would happen.
I had a PCB laying around so I connected the 4 PWM leads to both drive motor transistors. Then assigned a PWM slider control to Digital port 1 on the EZ-B controller, wired the PWM and ground leads to a servo cable then connected a Roomba battery to the circuit board. The two stock drive motors were connected to the two jacks normally used for the drive motors and when a PWM signal was active on any of the corresponding leads, the motor would run. Naturally the motor speed can be controlled by moving the slider control. No other connections have to be made on the PCB in order to use the two drive motor H bridges. Here are a few pictures: