Busulfan, Cyclophosphamide, & Antithymocyte Globulin Followed by Stem Cell Transplant in Treating Hematologic Cancer

RATIONALE: Giving chemotherapy before a donor bone marrow transplant or peripheral 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 certain 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 after the transplant may stop this from happening. PURPOSE: This phase II trial is studying how well giving busulfan together with cyclophosphamide and antithymocyte globulin followed by donor stem cell transplant works in treating patients with hematologic cancer.