In a heavy saucepan, combine sugar and flour; gradually stir in water and vinegar until smooth. Bring to a boil; cook and stir for 2 minutes or until thickened. Cool completely. Meanwhile, cook pasta according to package directions; rinse in cold water and drain. Stir mayonnaise and mustard into the dressing. In a large bowl, combine the remaining ingredients. Add pasta and dressing; toss to coat. Cover and chill until serving. Store in the refrigerator.