For crust, combine crushed crackers, melted butter or margarine, and Parmesan cheese in a medium mixing bowl. Press mixture evenly on the bottom and about 1 inch up the sides of a 9-inch springform pan. Set pan aside.

For filling, beat softened cream cheese in a large mixing bowl until smooth. Add eggs all at once. Beat on low speed just until combined. Add tub cream cheese and vinegar or lemon juice, beating on low speed just until combined. Stir in sour cream, smoked salmon, and snipped dill.

Pour into crust-lined springform pan. Place the springform pan on a shallow baking pan on the oven rack. Bake in a 350 degree F oven for 30 to 35 minutes or until center appears nearly set when shaken.

Remove springform pan from baking pan. Cool cheesecake on a wire rack for 15 minutes. Use a small metal spatula to loosen crust from sides of pan. Cool 30 minutes more. Remove sides of the springform pan. Cool 1 hour; cover and chill at least 2 hours. Garnish with fresh dill sprigs and salmon caviar, if desired. Makes 16 appetizer servings.

Up to 1 day ahead, make and bake cheesecake. Cool, then cover and chill.