Place chicken between two sheets of heavy-duty plastic wrap; flatten to 1/2-inch thickness, using a meat mallet or rolling pin. Spinkle with salt and pepper; dredge in flour.
Melt margarine in a large nonstick skillet over medium-high heat. Add chicken, and cook 8 to 10 minutes or until done, turning once. Remove chicken from skillet, and keep warm.
Combine broth and cornstarch; stir in marmalade. Stir broth mixture into skillet, and cook, stirring constantly, until mixture is thickened. Stir in vinegar. Reduce heat to medium; add chicken, turning to coat. Cook 1 to 2 additional minutes or until thoroughly heated. Garnish with orange slices, if desired.