Place popcorn and peanuts in a large bowl; set aside. In a large heavy saucepan over medium heat, bring sugar and corn syrup to a rolling boil, stirring occasionally. Remove from heat; stir in peanut butter and vanilla. Quickly pour over popcorn mixture and mix well. When cool enough to handle, quickly shape into ten 2½-inch balls. Let stand at room temperature until firm; wrap in plastic wrap. Yields 10 popcorn balls.