Couple more links: http://www.openservo.org/ (see: http://www.openservo.com/StepByStep) and http://code.google.com/p/zosupermodified/
These designs are intended to replace the control board inside an RC servo to give it full positional feedback. The "openservo" hardware is available for purchase but the "supermodified" hardware appears to have fallen off the internet unfortunately 