Mix crumbs and margarine; press onto bottom of 9-inch spring-form pan.
Bake at 350°, 10 minutes.
Soften gelatin in water; stir over low heat until dissolved.
Combine cream cheese and sugar, mixing at medium speed on electric mixer until well blended.
Gradually add gelatin, milk and peppermint candy, mixing until blended; chill until thickened but not set.
Fold in whipped cream and chocolate; pour over crust.
Chill until firm.
Garnish with additional whipping cream, whipped, combined with crushed peppermint candy, if desired.