Donor Stem Cell Transplant After Busulfan, Fludarabine, Methylprednisolone, and Antithymocyte Globulin in Treating Patients With Bone Marrow Failure Syndrome

RATIONALE: Giving low doses of chemotherapy and antithymocyte globulin before a donor stem cell transplant helps stop the growth of abnormal cells. It may also stop the patient's immune system from rejecting the donor's stem cells. The donated stem cells may replace the patient's immune cells and help destroy any remaining abnormal cells (graft-versus-tumor effect). PURPOSE: This phase II trial is studying how well a donor stem cell transplant works after busulfan, fludarabine, methylprednisolone, and antithymocyte globulin in treating patients with bone marrow failure syndrome.