If you can do a little breadboard wiring and reprogram the pwm port you might want to take a look at the SN754410 DC motor drive chip. It can control 2 motors. 2 inputs control the direction and the enable line can control speed by driving it with a fixed frequency PWM. Vary the duty to control power. You'll have to modify the default code to change the hardware PWM for the frequency and then add code to change the duty.
This app note is for basic but gives an example.
http://kronosrobotics.com/an101/DAN101.shtml The same chip can controll stepper motors too. It could also drive Fets for higher power.There are also chips that can generate the PWM and monitor current for curent limiting. They are harder to implement. Note the warning about the 10000K resisters inline on the inputs. This chip is not isolated and if it fails there could be drive voltage on the inputs. The resistors povide some protection.