In a 2 quart bowl, combine sugar and milk. Add butter or margarine. Cook, uncovered, on high for 5 minutes until mixture comes to a full rolling boil, stirring twice. Reduce setting to medium and cook 6 minutes, stirring twice. Stir in chips until melted. Add marshmallow crème, vanilla, and nuts and stir until well combined. Pour into a buttered 9x9 inch baking pan. Cool. Cut into squares.