Chill a small mixing bowl and beaters. In the top section of a double boiler, soften gelatin in the melted concentrated orange juice. Place over hot water, and stir until the gelatin is completely dissolved. Remove from heat and stir in the sugar and vanilla. Using cold beaters, beat dry milk and water until soft peaks form. Add the lemon juice and beat until stiff. Fold in orange juice mixture. Spread on 12 graham crackers. Top with the remaining crackers. Wrap individually; freeze until firm about 2 hours. Exchanges per sandwich: 1/2 nonfat milk, 1 fruit, cal 89, chol 17, pro 3, fat 1, na 121, k 181, 1/2 tsp sugar (8 cal) per serving. Makes 12 servings.