OK, pretty simple stuff, I happened to have this video around. I send servo positions (as strings not bytes) from the PC program to the arduino, which runs a PMW to drive the motor controller. I wrote the program originally to test servos. I'm thinking about adding a RPM sensor and eventually measure battery voltage and current and all that, eventually...
Since it's pretty simple to do, and has probably been done hundreds of times before, I'm not going to explain too much here, unless anyone is interested.
http://video.google.com/videoplay?docid=-1636085435135113197&hl=en
-Z-