Preheat oven to 350 degrees F (175 degrees C). Place brisket in 9x13 inch pan.
In a medium bowl, combine dressing, soup mix, and cranberries. Pour over brisket, and cover pan with foil.
Cook for 3 to 4 hours, or until brisket is extremely tender. Brisket will get very dark/caramelized; this adds flavor, and doesn't mean that you have overcooked it.