RATIONALE: Giving chemotherapy, such as fludarabine, busulfan, and cyclophosphamide, before a donor peripheral blood stem cell transplant helps stop the growth of cancer 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 high-dose cyclophosphamide together with tacrolimus and mycophenolate mofetil after transplant may stop this from happening.