On February 22, 2000, about 1735 Eastern Standard Time, a Piper PA-28-181, N8366N, was substantially damaged while maneuvering near Center Harbor, New Hampshire. The certificated private pilot, and pilot rated passenger received minor injuries. Visual meteorological conditions prevailed for the flight that originated from Alton Bay Seaplane Base, Alton Bay, New Hampshire; destined for Laconia Municipal Airport, Laconia, New Hampshire. No flight plan was filed for the personal flight conducted under 14 CFR Part 91. The pilot stated: "...We took off from Alton Bay and decided to fly over lake winnipesaukee on a scenic ride (again, I was pilot-in-command and the instructional part of the flight had ended). I flew low above the lake staying well clear of any persons or property (1000 ft or more). We only saw 2 snowmobilers and stayed well clear of them as well as all "Bob" houses. We were approaching Center Harbor and about to turn back home to Laconia airport when we hit the snow covered lake with our wheels and plowed to a stop. At the time I believed I was maintaining 100 ft agl and cruise speed of approx. 110 kts..." The pilot rated passenger stated: "...He leveled off at about 100 feet AGL, and asked me what altitude would be good. I quoted to him the provisions of FAR 91.119...While flying over the lake he observed a snowmobile approaching ahead, so he climbed, presumably to maintain separation, then when the vehicle passed, he began a slow descent. After he had descended awhile I looked out the right side window. When I recognized our relative altitude, I realized we were dangerously low. When I looked forward I noticed that Mr. Eifert was looking out my side window. I moved to take the yoke to climb, but we contacted the surface before I could take the controls..."