Weather conditions were fine with a strong South-Easterly wind blowing, greater than 20 knots. The latter portion of the instructional flight consisted of practice auto rotational approaches and landings. The entry height for the manouevre was progressively reduced each time until the final entry at 100 feet above ground level and 60 knots indicated airspeed. The low rotor RPM warning horn sounded after entry into the descent. At about 30 feet altitude, both pilots became aware of a very high rate of descent. The instructor took control to ensure a level attitude at touchdown but he was unable to avoid a heavy landing. The main rotor severed the tail boom and the helicopter rolled over onto its right side. Both pilots climbed out of the left doorway.