I got my order of Raspberry Pis this week. This weekend I sat down and figured out how to use the Pi to control a Jaguar. Here I'm just typing text commands at the command prompt which set the PWM pulse width going to the Jaguar. I found the right numbers using a cheap RC servo, so the Jag may use slightly different values for full forward and reverse. 600 microseconds is full reverse. 1500 microseconds is stop. 2400 microseconds is full forward.
Video
here.