In a large saucepan, combine water, 1/2 c sugar, grated lemon peel and vanilla. Set pan over medium heat and whisk until sugar dissolves and mixture simmers.
Add whole peaches and poach 5 minutes. Remove pan from heat and let peaches cool in syrup for 5 minutes. Cover and refrigerate 30 minutes, until cool.
Meanwhile, in a blender, combine raspberries, remaining sugar and lemon juice. Puree until smooth, then strain mixture through a fine sieve to remove seeds. Set aside.
Cut peaches in half. Divide ice cream or yogurt evenly into bowls. Garnish with a peach half, then spoon raspberry sauce over top. (Discard peach syrup.)