Preheat the oven to 400 degrees. Spread the potatoes in a roasting pan. Combine 4 tablespoons of the olive oil with the garlic, salt and pepper and drizzle over the potatoes. Roast about 45 minutes, turning once or twice during cooking.
With the remaining oil, mix with the vinegar, sugar and parsley.
Allow potatoes to cool completely. Put potatoes and vegetables into a salad bowl. Toss lightly with the salad dressing. Cover and chill before serving.