The study proposes the use of Fludarabine, Busulfan, Anti Thymocyte Globulin Rabbit (ATG) and Total Body Irradiation as a preparative regimen before hematopoietic stem cell transplant from unrelated donor peripheral blood stem cells (PBSC). The hypothesis states that the 100 day mortality after this type of transplant will be significantly below the accepted standards, which is about 30% for unrelated donors.