I found this recipe on allrecipes.com; it makes quite a bit (I used a half recipe tossed into 50 servings of salad) and tastes great!
1-3/4 cups red wine vinegar
2.5 cups white sugar
5 cups vegetable oil
2 large onions, minced
1.5 tablespoons ground mustard
1.5 tablespoons salt
1-1/4 teaspoons ground pepper
Combine all ingredients in a blender and process until smooth.
Into the Wild 