adding PWM to this great motor control:

This works GREAT, for my Sparkfun 100:1 mini gearmotor. I'm curious, instead of 2 digital pins, could I use 2 analog pins and control the speed with PWM?

Why not give it a try?

Okay, I just didn't want to hurt anything...

It will not hurt anything ,However just don;'t power you motor via. the arduino board power it from external power source and then configure your analog ports to act as output like the digital pin's.

Thanks, controlling the motor via PWM could be very useful.

"Useful" It's "Indispensable" tool.