Thanks to KeyserSoze's AWESOME alpha mesh for Warlokk's adult D model, I've made a couple of dresses suitable for your vampire-types. Get the mesh here:
http://www.insimenator.org/showthread.php?t=37713 I have accessorized in the screenshots with Maxis jewelry from Bon Voyage, but the file that you download will be for the dresses only. Enjoy!