Combine water and 3/4 cup sugar in a small saucepan; stir well. Bring to a boil, and cook 1 minute or until sugar dissolves, stirring constantly. Pour into an 11 x 7-inch baking dish, and chill.
Place 2 cups raspberries, 1/3 cup sugar, and vinegar in a food processor, and process until smooth. Strain through a sieve into a bowl; discard seeds. Cover raspberry mixture, and chill.
Add lemon juice and orange juice to chilled sugar syrup in baking dish; stir with a wire whisk until blended. Freeze 4 hours or until firm.
Place peach halves, skin sides up, on a jelly-roll pan. Bake at 450° for 4 minutes. Let cool, and peel off skins.
Place 1 1/2 tablespoons raspberry mixture in each of 6 dessert dishes; top with 2/3 cup sorbet and 2 peach halves. Sprinkle with lemon rind. Garnish with raspberries and mint sprigs, if desired.