Help Needed: Temperature control using PID

Hi

I am implementing PID to control temperature in a Box. Box has to maintain constant 32 degrees, Box contains steel walls, rotating pump, some plastic tubes. How to implement the PID? How to write code or analyse the PID? How to calculate the constants for P, I, D? what are all factors we have to consider? Please guide me how to implement without MATLAB. any free versions simulators for PID is available. i am writing in c.

Victory