While practicing a "power off 180 degree accuracy landing," the certificated private pilot became distracted in the traffic pattern by a converging airplane on approach to a different runway at the same airport. The accident airplane touched down with the landing gear retracted, and sustained substantial damage to the fuselage. The accident pilot had not lowered the gear on the downwind leg; instead he intended to lower the gear on final, when "he was sure [he] had the runway made." According to the airplane's information manual, the accident airplane was equipped with an audio warning system which was designed to sound whenever the throttle was retarded below 12 inches of manifold pressure. The accident pilot stated that he did not notice the landing gear warning tone until after the airplane stopped on the ground. Most of the accident pilot's instruction in complex airplanes was not conducted in the accident airplane.