Low-Dose or High-Dose Conditioning Followed by Peripheral Blood Stem Cell Transplant in Treating Patients With Myelodysplastic Syndrome or Acute Myelogenous Leukemia

RATIONALE: Giving chemotherapy, such as fludarabine phosphate, busulfan, and cyclophosphamide, and total-body radiation therapy before a donor peripheral stem cell transplant helps stop the growth of cancer cells. It may also 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. It is not yet known whether low-dose chemotherapy and total-body radiation therapy is more effective than high-dose chemotherapy in treating patients with myelodysplastic syndrome or acute myeloid leukemia. PURPOSE: This phase III trial is studying low-dose conditioning to see how well it works compared to high-dose conditioning followed by peripheral blood stem cell transplant in treating patients with myelodysplastic syndromes or acute myeloid leukemia