To prepare crust, combine crushed crackers, 1/4 cup margarine, and sugar in a mixing bowl. Press mixture firmly in a 9" pie pan. Chill one hour, or until firm. In a small saucepan, combine walnuts, remaining margarine, and sugar. Cook until melted and mixture comes to a boil. Boil 30 seconds. Spread on the bottom of the crust. Cool. In a mixing bowl, combine milk and pudding mixes. Mix until smooth. Mixture will be thick. Fold in pumpkin and pumpkin pie spice. Mix well. Gently stir in six ounces whipped topping. Spread over the nut layer. Refrigerate four hours, or until set. Spread with remaining whipped topping.