Bring large pot of water to boil. Add potatoes, and cook for about 10 ? 15 minutes, or until tender. Drain, and set aside to cool. Meanwhile, in large bowl, stir together salad dressing, mayonnaise, green onions, dill, mustard, lemon juice, and pepper. When potatoes are cooled, stir into bowl until coated. Refrigerate for a couple of hours to blend flavors before serving.