The recently purchased ultralight was taxied for about 40 minutes prior to the new owner trying his first flight. He had been advised by the former owner to make short hops at low altitude during a familiarization period. The former owner wanted to be present for this period because the new owner had no aviation experience. The new owner took off on his first flight without the instruction of the short hop period of familiarization. The takeoff went OK and the ultralight proceeded downwind to base in a controlled level flight. The turn to final approach was overshot and the ultralight angled back to 40 degrees off the runway heading. Over a tree he was heard to throttle back to descend, then to accelerate and decelerate. At this time the ultralight was seen to nose down and dive into the ground from about 100 feet above ground level at an angle of about 30 degrees. The aircraft was destroyed and the pilot fatally injured on impact. The engine was started and run at various power settings for 10 minutes in a test after the accident.