Place cereal in large bowl; set aside. In a 1-quart microwave-safe bowl, combine chocolate pieces, peanut butter and margarine. Microwave on high 1 to 1 1/2 minutes or until smooth, stirring after 1 minute. Stir in vanilla. Pour over cereal, stirring until all pieces are evenly coated. Place cereal mixture and sugar in a large resealable plastic bag. Shake until all pieces are well coated. Spread on waxed paper to cool. Store in a resealable plastic bag or other airtight