In a large bowl or using an electric mixer, combine cake and pudding mixes, eggs, sour cream, water, rum flavoring, butter and poppy seeds. Blend on a low speed, then beat at a medium speed for 5 minutes.
Pour batter into a well-greased and lightly floured Bundt pan.
Bake at 350 degrees for about 45 minutes, or until cake tests done. Remove from oven and cool in pan for 15 minutes. Turn onto cake rack and cool completely.
Sift a light dusting of powdered sugar over cake or prepare a glaze.