To prepare crust, combine crumbs, margarine, and sugar in a mixing bowl. Press mixture firmly in a 10" glass pie dish. Microwave on high for one and half minutes, rotating dish once during cooking time; set aside. Meanwhile, to prepare filling, mix cream cheese in a 2-quart glass bowl until smooth. Add sweetened condensed milk, egg whites, and lemon juice. Mix well. Microwave on medium-high for eight minutes, stirring every four minutes with a wire whisk until smooth again. Pour mixture into crust. Microwave again on medium for eight minutes longer, or until center is set, rotating dish once during cooking time. Let cool slightly. To prepare topping, combine sour cream, sugar, and vanilla extract. Mix well and spread evenly on top of cheesecake. Chill for three hours, or until set.