Anyone who watched the Olympics in August knows that the world is full of oddball sports that few of us in America have ever heard of. Modern pentathalon, anyone? Now try this one on for size: tree climbing. At the Twin Pines division of the New England Tree Climbing Association in Danville, Vt., instructor Al Manning will teach you how to master an activity you enjoyed as a child. Only here, it's on a much grander scale. Students use ropes and harnesses to scale pines up to 80 feet above the ground. If you got that high as a kid, you don't belong in the school; you belong in a zoo.