In a small saucepan, sprinkle gelatin over 1 cup cold water; let soften, 5 minutes. Place over low heat, and cook until gelatin has dissolved, 3 to 4 minutes. (When rubbed between your fingers, it should feel smooth.) Add sugar, stirring gently until dissolved, 2 to 3 minutes; remove from heat.
Transfer gelatin mixture to a medium bowl; gradually stir in juices. Pour into a 1 1/2-quart (6-cup) Bundt pan, and skim any foam from surface. Refrigerate until firm, at least 3 hours and up to 1 day.
To unmold, dip bottom of pan (do not submerge) briefly into hot water; invert onto a serving platter, and shake firmly to release. Serve.