For crust, in a medium mixing bowl stir together the crushed graham crackers and melted margarine or butter until crackers are moistened. Press mixture onto bottom of a 9-inch springform pan. Refrigerate while preparing filling.
For filling, in a food processor bowl or blender container combine half of the ricotta cheese, half of the cream cheese, half of the pumpkin, and half of the milk. Cover and process or blend until smooth. Transfer to a large mixing bowl. Repeat remaining ricotta, cream cheese, pumpkin, and milk.
In a small saucepan sprinkle the gelatin over orange juice; let stand 5 minutes. Cook and stir over low heat until gelatin is dissolved. Stir into pumpkin mixture. Stir in the orange peel, granulated sugar, brown sugar, vanilla, and the pumpkin pie spice. Pour mixture into chilled crust. Cover; refrigerate for at least 4 hours or until firm.
To serve, loosen crust from sides of pan; remove sides of pan. Cut into wedges. If desired, garnish with whipped topping and sprinkle with additional pumpkin pie spice.