In a medium bowl, mix the berries, sugar and rum.
In a trifle dish or a clear bowl, lay down 1/2 the pound cake chunks, top with half the berries and half the whipped cream, spreading each layer out so you can see them nicely on the sides of the dish. Repeat the process with the other half of the ingredients, sprinkle the top with a little powdered sugar and garnish with some fresh mint.