On September 7, 2000, at 0755 Eastern Daylight Time, a Piper PA-60-601P, N601WK, was substantially damaged during takeoff at the Northampton Airport (7B2), Northampton, Massachusetts. The certificated commercial pilot and passenger were not injured. Instrument meteorological conditions prevailed and an instrument flight plan was filed for the personal flight conducted under 14 CFR Part 91. The pilot reported in a telephone interview that 7B2 consisted of a single runway oriented on a 140/320 degree heading. The taxiway, which intersected Runway 14 at its midpoint, was oriented on a 120 degree heading. The pilot had parked at the fixed base operator (FBO), located south of Runway 14, when he arrived at the airport the previous day. Before departure from 7B2, the pilot instructed the passenger to "walk the length of the runway" and observe any obstructions, because the weather was "foggy, with 500-1,000 feet visibility." According to a written statement submitted by the pilot, he said: "I taxied to the asphalt pad by the FBO, completed my run-up and received clearance to depart from Bradley Approach. We were relatively lightly loaded, with about 100 gallons of gas, two people and no bags, or about 700 pounds under gross and with the "balance" right in the middle of the envelope. I expected about a 1500' takeoff roll given the weight, the 'Superstar I' engine modification, and the cool (60 degree) sea level (122') environment. I had the approach plate (NOS) on my clipboard on my lap and reviewed the small diagram, but only 'saw' the 14-32 runway." "I took what I thought was the runway and accelerated for takeoff. As we hit about 80 knots (rotation was to be at 95), I realized to my dismay that we were actually on the 1000' long taxiway angling at a heading of 120 degrees into about the middle of Runway 14 and not on the runway, as I had believed." "I immediately chopped the power and applied maximum braking. I attempted to make the 20-degree turn to line up with the runway where the taxiway intersected, but was primarily focused on not ground looping or cartwheeling. We missed the runway, but I got the plane turned to 140 degrees on the wet grass just at the very edge of the field, with the left wing hitting the brush along the edge. I almost thought that we would be able to stay in the runway environment, when the left wing hit an 8-10' tree and we spun down a 10' slope, crossed a dirt road, lost our gear, and slid into a cornfield. I was able to get the engines shut down, mags, fuel, mixtures and battery off by the time we stopped. There was no fire despite losing the 30 gallons from the left wing and a smaller fuel leak from the right wing." In a subsequent telephone interview, the pilot stated that he aligned his horizontal situational indicator (HSI) to a magnetic heading of 120 degrees while he was parked at the FBO. He reported that he did not check the HSI again before takeoff. According to the airport manager at 7B2, the taxiway which the pilot began his takeoff from was painted with a 120 degree marking and a 15 foot long yellow centerline. The taxiway extended from a compass rose painted on the surface. Additionally, Runway 14/32 was "clearly painted," including centerline markings, threshold markings, and runway identification numbers. Runway 14 was 3,500 feet long and 50 feet wide, with a 300 foot displaced threshold. The runway lights were non-standard, but "worked well." The weather reported at 0755, at an airport 9 miles away was: wind from 320 degrees at 2 knots; visibility 1/16 mile with fog; sky partially obscured; ceiling 200 feet overcast; temperature 43 degrees F; dew point 43 degrees F.