PREHEAT oven to 350°F. Place granulated sugar, margarine, eggs and vanilla in medium bowl; stir until well blended. Add graham crumbs and walnuts; mix well.
SPREAD into greased 8-inch square baking pan.
BAKE 30 to 35 minutes or until toothpick inserted in center comes out clean. Cool completely in pan on wire rack. Sprinkle with powdered sugar. Cut into 16 squares to serve.