Beat whipping cream and sugar until peaks form.Set aside. Mix the mascarpone cheese, pumpkin and spice; beat until filling is smooth then fold in whipped cream. Line bottom of 9-inch springform pan with 2 3/4-inch high sides with one package of ladyfingers,overlapping and crowding to fit. Use pastry brush and brush the ladyfingers with 2 tablespoons of Grand Marnier. Spread half of filling over. Repeat with second package ladyfingers, remaining 2 tablespoons Grand Marnier, and remaining filling. Smooth. Wrap tightly with plastic, then foil. Chill overnight. To unmold, run knife around inside edge of pan. Release pan sides; sprinkle with gingersnap cookies.