In a heavy saucepan combine sugar, margarine and evaporated milk. Bring to a full rolling boil, stirring constantly. Boil 5 minutes over medium heat, stirring constantly to prevent scorching. Remove from heat. Stir in chocolate pieces until melted. Add marshmallow creme, nuts, and vanilla. Beat until well blended. Pour into a greased 9x13-inch pan. Cool at room temperature and cut into squares.