THE PILOT SAID THAT DURING HIS IFR FLIGHT THE ACFT HAD ACCUMULATED ABOUT TWO INCHES OF RIME ICE ON THE LEADING EDGES OF THE WINGS AND HAD LOST ABOUT 15 KNOTS AIRSPEED. HE ESTABLISHED THE ACFT ON THE LOCALIZER FOR THE APPROACH AND WHEN HE WAS 1.9 MILES FROM THE AIRPORT AND 500 FEET AGL HE REDUCED HIS AIRSPEED TO 100 KNOTS AND LOWERED THE GEAR. THE ACFT COLLIDED WITH TREES THEN THE TERRAIN ABOUT 800 FEET SHORT OF THE RUNWAY.