To prepare crust, combine crumbs, margarine, and sugar in a mixing bowl. Press mixture firmly in a 9" pie pan. Spread crumb mixture evenly in pie pan. Chill 1 hour, or until firm. Or, bake in a 375 oven for 10 minutes or until edges are brown. Cool on rack before filling. To prepare filling, combine gelatin and water in a saucepan. Let stand one minute. Over low heat, stir until gelatin is completely dissolved. Cool. In a mixing bowl, combine chocolate, sweetened condensed milk, gelatin mixture, and vanilla extract. Mix well. Fold in whipped topping. Pour into crust. Chill three hours or until set.