1. Place ham on rack in open roasting pan. Insert meat thermometer into center of ham. Bake ham in 325°F. oven 1 1/2 to 2 hours, until meat thermometer reaches 130° to 140°F.
2. About 40 minutes before ham is done, make glaze: In 1-quart saucepan over low heat, heat pineapple preserves, apple jelly, horseradish, and mustard until jelly melts, stirring often. During last 30 minutes of baking, brush ham frequently with glaze.
3. Meanwhile, in small bowl, combine brown sugar, maple syrup, and cinnamon and set aside. In 12-inch skillet over medium heat, heat 1/2 inch water and squash to boiling. Reduce heat to low; cover and simmer about 10 minutes, until squash is fork-tender; drain.
4. To squash in skillet, add 4 tablespoons butter or margarine {1/2 stick) and half of brown-sugar mixture. Over medium heat, cook mixture, stirring gently, until butter and brown sugar melt and squash is glazed; keep warm.
5. In 10-inch skillet over medium-high heat, in 4 tablespoons hot butter or margarine (1/2 stick), cook apples until tender, about 5 minutes, stirring often. To apples, add remaining brown-sugar mixture, and continue cooking, stirring gently with rubber spatula, until brown sugar is melted and apples are glazed.
6. Place ham on warm large platter; arrange squash and apples around ham. Pour any remaining glaze over squash and apples.