Stir together sugar and water in a medium saucepan. Bring to a simmer over medium heat, stirring until sugar dissolves. Stir in cranberries, and cook, stirring occasionally, until cranberries pop and are softened, about 6 to 8 minutes. Stir in currant jelly, and cook, stirring often, until jelly melts. Remove saucepan from heat, and place in an ice-water bath. Stir occasionally until mixture cools to room temperature.