Combine water and sugar in a small saucepan. Bring to a boil, and cook for 30 seconds or until sugar dissolves, stirring constantly. Remove from heat, and stir in rum, lime rind, and lime juice. Cool to room temperature.
Combine peaches, grapes, and raspberries in a large bowl. Add the rum mixture, tossing to coat. Garnish with mint sprigs, if desired.