RATIONALE: Giving low doses of chemotherapy, such as fludarabine and cyclophosphamide, and radiation therapy before a donor bone marrow transplant helps stop the growth of cancer cells. Giving chemotherapy or radiation therapy before or after transplant also stops the patient's immune system from rejecting the donor's bone marrow stem cells. The donated stem cells may replace the patient's immune system cells and help destroy any remaining cancer cells (graft-versus-tumor effect). Sometimes the transplanted cells from a donor can also make an immune response against the body's normal cells. Giving tacrolimus and mycophenolate mofetil after the transplant may stop this from happening.