MIX crumbs, sugar and margarine until well blended; press firmly onto bottom and up side of 9-inch pie plate. Set aside.
PREPARE pudding mix as directed on package for pie filling, using 1-1/2 cups milk. Let stand 2 minutes. Gently stir in 1-1/2 cups of the whipped topping, the marshmallows and 1/2 cup of the walnuts. Pour into crust.
REFRIGERATE several hours or until chilled. Top with remaining 1/2 cup whipped topping and the remaining 1/4 cup walnuts just before serving. Store leftover pie in refrigerator.