Treatment of Single or Double Umbilical Cord Trans + Graft-versus-host Disease (GVHD) Prophylaxis w/ Tacrolimus & Mycophenolate Mofetil

RATIONALE: Giving chemotherapy and total-body irradiation before a donor umbilical cord blood transplant helps stop the growth of cancer and abnormal cells and helps stop the patient's immune system from rejecting the donor's stem cells. When the healthy stem cells from a donor are infused into the patient they may help the patient's bone marrow make stem cells, red blood cells, white blood cells, and platelets. Sometimes the transplanted cells from a donor can make an immune response against the body's normal cells. Giving tacrolimus and mycophenolate mofetil before and after transplant may stop this from happening. PURPOSE: To look at the ability of umbilical cord blood cells from one or two unrelated donors to serve as a source of stem cells for people needing a bone marrow transplant.