For syrup, in a small saucepan, combine sugar and the water. Cook and stir over medium heat until sugar is dissolved. Transfer to a small bowl or a 1-cup glass measure. Cover and chill for 1 hour.
In a large punch bowl, stir together cranberry juice, orange juice, pineapple juice, lemon juice, and chilled syrup. Slowly pour ginger ale down side of bowl; stir gently to mix. Serve over ice cubes. If desired, garnish with cranberries and lemon slices.