Combine 1 1/4 cups crushed gingersnaps, 1/4 cup ground walnuts, 6 tablespoons melted butter and 2 tablespoons sugar. Press evenly onto bottom and sides of 9-inch pie plate. Bake 8-10 minutes or until lightly browned. Cool completely on wire rack.
Combine brown sugar and gelatin in small heavy saucepan. Gradually stir in 1 cup eggnog. Heat over low heat, stirring constantly, until gelatin is completely dissolved. Remove from heat. Stir in remaining 1 1/2 cups eggnog. Refrigerate until slightly thickened. Beat whipping cream in small chilled mixer bowl until soft peaks form.
Using same beaters beat rum, brandy and vanilla into eggnog mixture. Fold in whipped cream. Pour into cooled Gingersnap Crust. Refrigerate several hours or overnight. Just before serving garnish with whipped cream and walnut halves (optional).