Simple Collision Sensor

I read another post, but can't seem to figure out exactly where the code lines go for registering a collision between 2 objects.

Say I have _sphere and _ground as sio2object types already. How would I go about giving them a collision sensor detection and callback to a function when they collide?

thx in advance

RESOLVED: Thanks!
http://forum.sio2interactive.com/sio2-engine-f3/collision-system-t62.htm