G-CSF mobilization of the donor's peripheral blood white blood cells will precede donor apheresis. A nonmyeloablative conditioning regimen of fludarabine and busulfan will be administered to patients prior to allogeneic peripheral blood stem cell infusions. FK506 and prednisone will be administered for graft versus host disease (GVHD) prophylaxis. Patients will be evaluated for engraftment, donor: host hematopoietic chimerism, toxicity, and hemoglobinopathy.