If you're still looking for PID control information, might I suggest the indutrial control tutorial from Parallax.

The code is for a Basic Stamp, but it's easy enough to port it to PBP, plus they have a very thourough explenation of the logic behind it.

If you're interested you can find it here: http://www.parallax.com/detail.asp?product_id=28156

The manual is available as a seperate download called ic.pdf

-Denny