In a small saucepan, combine the 1/4 cup light corn syrup, the margarine and brown sugar. Cook and stir over medium heat until the margarine melts. Combine the rice cereal and the syrup mixture, stirring until the cereal is well coated.
Using the back of a spoon, evenly press the cereal mixture over the bottom and up the sides of a 9-inch pie plate to form the pie crust; freeze about 10 minutes or until set
Meanwhile, in a small bowl, stir together the peanut butter, fudge sauce and the 3 tablespoons light corn syrup. Spread half of the peanut butter mixture over the bottom of the cereal crust.
Stir the vanilla ice cream to soften it slightly. Spoon the vanilla ice cream over the peanut butter layer, spreading it evenly. Drizzle the remaining peanut butter mixture over the ice cream; if the peanut butter mixture becomes too stiff to drizzle, stir in a few drops of the milk.