The pilot executed a VOR/DME instrument approach and descended below the published minimum descent altitude of 579 feet AGL. The airplane touched down half way down the runway and the pilot aborted the landing. A witness observed the airplane depart and maneuver at low level around the airport before he lost sight of the airplane. The airplane flew under a set of power lines and impacted fence posts and the terrain. The airplane's pitot static system head separated from the airframe during the impact sequence with the fence posts. The pilot stated a malfunction of the VSI and altimeter occurred during the instrument approach. No system failure was reported to the NTSB by the FAA coordinator. Testing of the pitot static system did not reveal any problems with the system. The passenger stated that the pilot attempted to fly around the airport at less than 100 feet in very poor visibility and that there were no instrument problems during the approach.