This study will determine if bone marrow stromal cells can be used as a graft for regeneration of bony defects. These cells have the ability to form new bone and to support the formation of blood. Stromal cells have been identified in other tissues, such as the dermis (underside of skin), spleen, thymus and fat, but it is not known whether these cells can make bone and support blood formation as well as bone marrow stromal cells.