In an ungreased heavy skillet, over medium heat, toast walnuts, stirring constantly, until golden, about 3 minutes. They should have lost their raw taste. Immediately transfer to a bowl to cool. After about 5 minutes, coarsely chop walnuts. Set aside. In a blender mix cheese, Port and cream to a smooth paste. Add grapes. Pulse until grapes are chopped and distributed throughout mixture. Scrape mixture into a serving bowl. Stir in chopped nuts. Cover tightly and refrigerate 30 minutes to overnight. Serve cool or at room temperature, garnished with walnut halves and grapes.