Pour cereal into large bowl and set aside. In 1-quart microwave-safe bowl, combine Hershey's chocolate chips, peanut butter, and margarine. Microwave on high one to one and a half minutes or until smooth, stirring after one minute. Stir in vanilla. Pour chocolate mixture over cereal, stirring till all pieces are evenly coated. Pour cereal into large glad lock bag with powdered sugar. Seal securely and shake until all pieces are well coated. Spread on waxed paper to cool.