 INDUCTION IB: Patients receive imatinib mesylate PO QD on days 1-35, cyclophosphamide IV over 30-60 minutes on days 1 and 28, mercaptopurine PO on days 1-28, cytarabine IV or subcutaneously SC on days 1-4, 8-11, 15-18, and 22-25, and methotrexate IT on days 8 and 22. 