On May 13, 2000, about 1430 Eastern Daylight Time, a Piper PA18-150, N9432P, was substantially damaged while landing at the Forest Hill Airport, Forest Hill, Maryland. The certificated private pilot was seriously injured. Visual meteorological conditions prevailed and no flight plan had been filed for the flight that originated at Donegal Springs, Pennsylvania. The personal flight was conducted under 14 CFR Part 91. According to a Federal Aviation Administration (FAA) inspector, the airplane was landing on Runway 31, a 2,650 foot long, 50 foot wide asphalt runway. During the landing roll, the airplane veered off the right side of the runway, and impacted a parked airplane. The pilot stated he entered the traffic pattern for Runway 31, after he observed the windsock indicated the wind direction was from the northwest at 5 to 10 knots. The pilot described the approach and touchdown as "normal;" however, he had "no recollection of events following touchdown." A witness at the airport observed the airplane on final approach with it's left wing down, "in a slip." After touchdown, the airplane yawed back and forth on the runway. The airplane then entered the grass area adjacent to the runway and struck the parked airplane. Winds reported at an airport about 15 miles south of the accident site, at 1448, were from 160 degrees at 5 knots. The pilot reported 183 hours of total flight experience; with 5 hours in tail-wheeled airplanes, all in the PA-18-150.