If there is no ground (or edge of window) immediately below the actor, then the actor is in the air (which is considered jumping). So. look for an object below the actor (at a vertical offset of half the actor's height). If the actor is allowed to walk on the bottom edge of the window (not always an actual object below the actor when standing or walking), then also check for a 'y' value of the world's height minus half the actor's height.

danpost, I think you missed the "kinect" part of the question :D 8bitorangejuice - I don't think there is anything that will directly tell you if someone is jumping, but consider what happens when you jump. First your head is at some height, then it goes up, then it goes back down. So, you could record the height of the head, and if it goes up significantly, assume they are jumping.

Dav, can you help me with the code? I am creating a game for a school event and need help with the coding of kinect; I am a complete novice with kinect sensoring...