On December 13, 2002, about 1830 eastern standard time, a Piper PA-601P, N141AJ, sustained minor damage during takeoff at the Manassas Regional Airport (HEF), Manassas, Virginia. The certificated commercial pilot was not injured. Night instrument meteorological conditions prevailed, and an instrument flight rules flight plan was filed for the personal flight conducted under 14 CFR Part 91. According to the pilot, he preflighted the airplane, identified no relevant anomalies, boarded, and then taxied to runway 34R. Once cleared for takeoff, he held the brakes, and advanced the throttles to 30 inches of manifold pressure. He confirmed the oil pressure and fuel flow indications for both engines were correct, and matched. He then advanced the throttles to 42 inches of manifold pressure, takeoff power, and initiated the takeoff roll. He used differential braking to maintain runway alignment until reaching 40 knots of indicated airspeed (KIAS), and then transitioned to the rudder. Approximately 65 KIAS, the pilot felt a shudder that seemed to come from the wheels, which he initially thought was caused by standing water on the runway. Within a second, he felt a second shudder, and started to have directional control problems. Because the airplane was "...well below rotation speed," he aborted the takeoff. He closed both throttles, and within 2 seconds, the airplane yawed left and departed the runway. On rain-soaked sod, the airplane slid approximately 1,000 feet before coming to a stop in a ditch approximately 300 feet to the left of the runway. A weather observation taken at the airport about 25 minutes after the accident, recorded the wind as 360 degrees at 8 knots, visibility 3 miles, temperature 36 degrees Fahrenheit, dew point 36 degrees Fahrenheit, and an altimeter setting of 29.75 inches of mercury. In addition, the pilot reported it had snowed 2 days before, and that it had rained steadily on the day of the accident. According to a Federal Aviation Administration inspector, examination of the engines and airframe revealed no preimpact failures or malfunctions. In addition, the airplane sustained minor damage during the accident sequence and substantial damage during recovery.