All patients in this study will receive imatinib mesylate by mouth for 9 days, unless the patient is known to be allergic or have symptomatic intolerance to the drug, or if the leukemia has failed to respond to imatinib. Fludarabine 40 mg/m2 by vein for 4 days (days -5 to -2), busulfan 130 mg/m2 by vein for 2 days (days -3 and -2), and ATG (Antithymocyte Globulin) 2.5 mg/kg by vein for 3 days (-3,-2 and -1).