Here is an interesting robot from wayneage that plays Pong using a NXTCam camera to track a ball in real time. The NXTCam continuously sends the location (coordinates) of the ball to the NXT brick. The robot keeps adjusting its position to hit the ball when it is close enough. Before the robot starts, the NXTCam is taught the colours to track using another program called NXTCamView (this is not shown in the video). As you can see it works quite well - nice work!