On February 18, 2006, at 1730 eastern standard time, a Cessna 421C, N98507, sustained substantial damage during landing on runway 32 (7,605 feet by 150 feet, asphalt) at the Indianapolis International Airport (IND), Indianapolis, Indiana. The airline transport pilot and the passenger were not injured. During the approach to landing, only the nose landing gear extended. The main landing gear remained in the wing wheel wells requiring the pilot to make a main gear up landing. The 14 Code of Federal Regulations Part 91 personal flight departed Salt Lake City, Utah, at 1110 mountain standard time and was en route to Cincinnati, Ohio, but diverted to IND to refuel. Visual meteorological conditions prevailed at the time of the accident. The flight was on an instrument flight rules (IFR) flight plan. The pilot reported that he intercepted the final approach course for the ILS to runway 32 about 8 nautical miles out at 170 knots. He lowered the landing gear handle. The nose landing gear lowered, but the main landing gear did not. The main landing gear indicator lights remained unlit. He cycled the landing gear handle three times without effect. He attempted to yaw the airplane and porpoise the airplane to get the gear down, but with no result. He executed the emergency gear extension procedures and actuated the nitrogen bottle, but without success. He did a fly-by of the control tower and the controllers confirmed that the main gear were still in the wings. He tried to get the gear down by pulling positive G's on the airplane, but it did not work. The pilot decided to land with the nose gear down and the main gear up. On short final at 100 feet above ground level, he put the engine mixture to idle cutoff. At 50 feet he raised the flaps. The airplane skidded on the runway for 1,500 to 2,000 feet and then the nose landing gear collapsed. The inspection of the airplane revealed that the main landing gear were in the retracted position during landing. The nose gear was extended and collapsed during landing roll. During aircraft recovery, the main landing gear extended to a down and locked position when the aircraft was raised up. The inspection of the blow down bottle revealed that the valve had been actuated and the bottle was empty. The inspection of the landing gear system revealed that there were no leaks in the hydraulic lines. The landing gear were cycled successfully numerous times with no anomalies. The blow down bottle was tested and the gear extended to the down and locked position. There was no mechanical damage to the mechanical uplocks. The inspection of the landing gear system did not reveal any anomalies to the landing gear system that would have prevented normal operation.