Combine sugar and water in a large saucepan, and bring to a boil, stirring until the sugar dissolves. Remove from heat, and cool completely. Add orange juice, Champagne, and lime juice; pour into an 11 x 7-inch baking dish. Cover and freeze for 8 hours or until firm. Remove mixture from freezer; let stand 10 minutes. Scrape the entire mixture with a fork until fluffy, and garnish with lime wedges, if desired.