Cover Macaroni with water and cook until almost done, drain well. In bowl, melt margarine in microwave. Stir in flour. Stir in milk. Salt and Pepper to taste. Pour cubed cheese into milk mixture and microwave at 30 second intervals until melted, stirring often. Stir in cooked macaroni. Place in oven safe dish and bake, uncovered, at 350 for twenty minutes.