According to the pilot, he was flying from one airport to another using a highway as a reference. He saw an airport that he thought was the destination airport, and made a straight-in approach for landing. Just before touching down, the pilot realized that he was not landing at the correct airport, and was landing on a snow-covered and unplowed private airstrip. He stated that he did not have time to go around, and landed on the snow. The airplane crossed a snow machine track and nosed over. The engine firewall and both wings sustained substantial damage.