Preheat oven to 400 degrees F. Crush pretzels with rolling pin. Mix with sugar and melted margarine (or butter). Press into bottom of 9x13-inch baking pan. Bake 5 minutes. Cool. Beat cream cheese and sugar till fluffy. Mix in whipped topping. Fold in drained pineapple. Spread mixture onto cooled pretzel crust. Dissolve gelatin in boiling water. Mix in frozen raspberries. Place gelatin in refrigerator till syrupy. Pour over cream cheese layer. Refrigerate till set. Garnish with whipped cream.