In medium bowl, soak porcini mushrooms in boiling water for 20 minutes. Drain, reserving 1/4 cup liquid. Set mushrooms aside.
In small bowl, combine reserved mushroom liquid, broth, vinegar and cornstarch; blend well. Set aside.
Melt 1 tablespoon of the margarine in large skillet or wok over medium-high heat. Add beef strips, salt and pepper; cook and stir 2 to 3 minutes or until beef is browned. Remove from skillet; cover to keep warm.
In same skillet, melt remaining 1 tablespoon margarine over medium heat. Add porcini and cremini mushrooms; cook and stir 3 minutes.
Stir broth mixture until smooth; add to skillet. Cook and stir until sauce is thickened and bubbly. Add beef and tomatoes; cook and stir until thoroughly heated. Sprinkle with parsley.