Preheat oven to 350°F Spray 9" by 3" springform pan with nonstick cooking spray.
In food processor with knife blade attached, blend gingersnaps, walnuts, and 1/4 cup sugar until finely ground; stir in margarine or butter. Press mixture onto bottom and 2 1/2 inches up side of springform pan; set aside.
In small bowl, with mixer at high speed, beat egg whites until foamy. Gradually beat in 3/4 cup sugar until soft peaks form; set aside.
In large bowl, with same beaters and with mixer at medium speed, beat egg yolks, pumpkin, cream cheese, cinnamon, allspice, ginger, cloves, and 1/2 teaspoon nutmeg until well blended. Fold egg-white mixture into cream-cheese mixture; pour into springform pan. Bake 1 hour & 30 minutes or until knife inserted 1 inch from edge of cheesecake comes out clean. Cool cheesecake in pan on wire rack.
In small saucepan, mix eggnog, cornstarch, and 1/8 teaspoon nutmeg. Over medium heat, heat to boiling. Reduce heat to low; simmer 1 minute or until mixture thickens. Let stand 10 minutes to cool slightly. Remove side of springform pan from cheesecake; spread eggnog mixture over cheesecake. Garnish with walnuts. Refrigerate cheesecake at least 4 hours or until well chilled.