Putting PID into a microcontroller is dead easy. Designing and tuning the PID is a job for a superspecialist. Embedded systems magazine (www.embedded.com) had some excellent articles on the subject, unfortunately they are not included in the web archive (at least I could not find them). I would contact them and buy the 2 (or was it 3) back issues, that series of articles is the best I have seen, I almost believe that with those articles in hand I could design a PID.

Erik