In a small bowl, mix together crumbs and sugar; stir in butter. Press mixture firmly and evenly against bottom and side of 9-inch pie pan, building up slightly around rim. Bake in a preheated 350? F oven for 5 minutes. Cool on wire rack.
To prepare filling: sprinkle gelatin on water to soften. In a 1-quart saucepan, mix together sugar, cornstarch and salt. Gradually stir in eggnog. Cook over medium heat, stirring constantly until thickened. Cook 2 additional minutes. Remove from heat and stir in softened gelatin until dissolved. Divide filling in half. Add melted chocolate and vanilla to one half and pour into crust. Allow remaining half to cool; then add rum extract. In a chilled bowl, whip cream until stiff; fold in rum-flavored filling. Carefully spoon over chocolate layer. Chill.
To prepare topping: in a chilled bowl, whip cream until stiff; fold in confectioners' sugar. Spread over pie and sprinkle with grated chocolate.