HEAT oven to 325°F. Line 13x9-inch pan with foil, with ends extending over sides of pan. Finely crush 24 cookies. Melt 1/4 cup margarine; mix with crumbs. Press onto bottom of prepared pan.

BEAT cream cheese and sugar with mixer until blended. Add sour cream and vanilla; mix well. Add eggs, 1 at a time, beating after each just until blended. Chop remaining cookies. Gently stir into batter; pour over crust.

BAKE 45 min. or until centre is almost set. Cool. Meanwhile, microwave chocolate and remaining margarine in microwaveable bowl on HIGH 1 min.; stir until smooth. Cool slightly; spread over top of cheesecake. Refrigerate 4 hours. Use foil handles to lift cheesecake from pan before cutting to serve.