Combination Chemotherapy Followed by Donor Bone Marrow Transplant or Peripheral Stem Cell Transplant in Treating Patients With Hematologic Cancer or Genetic Disorders

RATIONALE: Giving chemotherapy drugs, such as fludarabine and melphalan, before a donor bone marrow transplant or peripheral blood stem cell transplant helps stop the patient's immune system from rejecting the donor's stem cells and helps stop the growth of cancer or abnormal 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. PURPOSE: This phase II trial is studying how well giving combination chemotherapy followed by donor bone marrow transplant or peripheral stem cell transplant works in treating patients with hematologic cancer or genetic disorders.