Marvelous Fruit Mixup

In large bowl, stir 3/4 cup boiling water into gelatin to dissolve completely. Add ice cubes. Stir constantly 3 to 5 minutes until mixture thickens slightly. Using slotted spoon, remove any unmelted ice. Stir sour cream into gelatin until blended. Set aside 1/2 cup pineapple, 1/4 cup mandarine oranges and 1 tablespoon walnuts for garnish. Stir remaining fruit and walnuts into gelatin along with all marshmallows. Pour into 8 inch square baking dish. Top with reserved fruit and walnuts. Refrigerate at least 4 hours or overnight until firm. Cut into squares to serve.