Put the water, sugar, lemon juice and vanilla pod into a wide saucepan and heat gently to dissolve the sugar. Raise the heat to medium-high and bring the pan to a boil for about 5 minutes, then turn the heat down to a simmer.
Cut the peaches in half and add to the sugar syrup. If all of the peaches do not fit into the saucepan at once, you may do this step in batches. Poach the peach halves for about 2 to 3 minutes on each side until cooked. Remove peach halves with a slotted spoon and peel off their skins. Set aside to cool.
To make the raspberry sauce, put the raspberries, confectioners sugar and lemon juice in a blender or a food processor and blend until liquid. Sieve to remove the seeds and pour the sauce into a measuring cup with a spout or a small pitcher.
To assemble, put 2 peach halves on each plate with a scoop of vanilla ice cream. Spoon the raspberry sauce over the top. Garnish with a sprig of mint.