Combine the sugar, water and ginger in heavy small saucepan. Stir over medium heat until sugar dissolves. Simmer 5 minutes. Remove from heat. Cover and let steep 1 hour. Strain. Puree mangoes in a blender. Pour into measuring cup. Return 3/4 cup puree to blender. Add 1/2 cup ginger syrup, vodka and ice cubes to blender. Blend until smooth. Serve in martini glasses.