Very good tutorial here for character creation:
Part 1: http://www.youtube.com/watch?v=DBdpIDGXEPU
Part 2: http://www.youtube.com/watch?v=oTI1A_FzOB8
Part two at 12:40 the lesson moves to collisions.
I am not a python expert but when you hover over any buttons in blender it shows the name of the python reference for it. When I tested a collision sensor it popped up with
Python: CollisionSensor.type bpy.data.objects["Cube"]
bpy is blender python the blender related code package.
There is also an interactive python display above the info panel (cant remember if it was introduced in the 2.6 series or not) which shows the python code which would do whatever activity you just did with the GUI.