The pilot reported that during an ILS Runway 7 Approach, he acquired the runway at 250 feet above the ground level, and performed a normal touchdown. After touchdown, the airplane continued down the 3,500 foot runway, and went off the end onto a soft overrun area, where the right main gear collapsed. The published decision height for the ILS approach was 208 feet. The 1335 EDT weather at the airport was reported, in part, to be 100 foot overcast, visibility 1/2 mile with fog, wind from 220 degrees at 15 knots.