Melt the margarine in large saucepan over low heat. Add marshmallows and stir until completely melted. Remove from heat. Add cereal, stir until well coated.
Using buttered fingers or a buttered spatula, press mixture evenly into a 13x9x2 inch pan coated with cooking spray.
When cooled, cut into 2 inch squares. Place squares on waxed paper an inch apart and dust with flour, turning squares to get all sides. Tap each square to remove excess flour and place on serving tray.