Preheat oven to 400 degrees F. Divide sweet potatoes between two 15 1/2" by 10 1/2" jelly-roll pans. In 1-quart saucepan, heat sugar, vinegar, margarine, salt and 1/4 cup water to boiling over high heat. Divide sugar mixture between jelly-roll pans; toss with potatoes to coat. Spread potatoes evenly in pans.
2. Roast potatoes 45 minutes or until very tender and glaze thickens, turning potatoes occasionally to coat.