Put chocolate chips in blender and add the boiling water. Blend for 1 minute, or until chips dissolve. Separate eggs. Add the yolks and the rum to chocolate mixture and blend for 1 minute. In another bowl, beat egg whites and cream of tartar until stiff. Fold chocolate mixture into egg whites. Spoon mixture into sherbet or parfait glasses. Chill thoroughly before serving. Garnish with whipped cream and crushed chocolate chips. Serves 6 to 10.