THE PILOT IN COMMAND'S INADVERTENT ACTIVATION OF THE LANDING GEAR SWITCH WHILE ATTEMPTING TO RAISE WING FLAPS DURING LANDING ROLLOUT, RESULTING IN COLLAPSE OF THE LANDING GEAR. CONTRIBUTING TO THE ACCIDENT WAS THE PILOT IN COMMAND'S DIVERTED ATTENTION TO THE RUNWAY TURNOFF POINT AND AN AIR CARRIER AIRCRAFT LANDING BEHIND HIM.