Preheat the oven to 325 degrees F. Score the skin and fat of the ham in a diamond pattern. Combine the pineapple juice, sarsaparilla, sugar and 1 cup water in a small saucepan. Heat over medium-high heat, stirring frequently until the sugar is dissolved. Place the ham in a shallow roasting pan. Baste with the pineapple juice mixture, and then bake until the ham reaches an internal temperature of 140 degrees F, 3 hours to 3 hours 30 minutes, basting with the pineapple mixture about every 30 minutes.