On May 29, 2004, approximately 1310 mountain daylight time, a Beech P-35, N7DR, registered to and operated by the pilot as a 14 CFR Part 91 local flight, experienced a loss of engine power shortly after takeoff from Havre, Montana. During the emergency landing, the aircraft was substantially damaged. Visual meteorological conditions prevailed at the time and no flight plan was filed. The commercial pilot and his three passengers were not injured. During a telephone interview and subsequent written statement, the pilot reported that just after lift-off from runway 25, he verified a positive rate of climb and retracted the landing gear. Shortly thereafter, the pilot felt a slight hesitation in the engine. The pilot switched the fuel selector when the engine suddenly lost power. The pilot noted that at this time the aircraft had drifted about 200 feet off of runway centerline. He immediately lowered the nose to maintain airspeed and extended the landing gear to re-land on the remaining runway. The aircraft touched down and the right main gear collapsed. The right wing contacted the runway surface and the aircraft spun around coming to rest near the end of the runway. After the aircraft was removed from the runway and placed in a secured location, a Federal Aviation Administration Inspector from the Helena, Montana, Flight Standards District Office, and a certified Airframe & Powerplant, Inspection Authorization mechanic inspected the aircraft. The mechanic reported that during the engine inspection, no evidence of a mechanical malfunction was noted. No fuel leaks were detected. The fuel selector was checked and found functional. Both fuel tanks were inspected for fuel and a trace amount of fuel was found in each fuel bladder. Inspection of the right wing inboard fuel sender found that the unit was unsecured. The left wings sender unit was secured. Both sender units were checked for cockpit indications. Both indicated empty when the float was extended to the bottom of the tanks and indicated fuel levels throughout the movement of the float from top to bottom. Approximately three gallons of fuel was put in the right side fuel tank to inspect for leaks. None were detected. The left wings piping structure had pulled out of the bladder connector during the accident sequence which allowed fuel to drain from the left fuel tank therefore fuel quantity could not be determined. The left and right side fuel tanks are not interconnected.