Soften gelatin in water. In a medium saucepan, mix egg yolks and 1/2 cup sugar. Stir in pumpkin, milk, cinnamon, nutmeg and ginger. Cook over medium heat until slightly thickened, stirring constantly. Remove from heat. Add softened gelatin; stir until dissolved. Chill until mixture begins to thicken. Beat egg whites until foamy. Gradually stir in remaining 1/2 cup sugar; beat until stiff, but not dry. Fold into pumpkin mixture. Spoon into pie crust. Chill until firm. Serve with whipped cream, if desired.