 DELAYED INTENSIFICATION 1 PART 2: Patients receive imatinib mesylate PO QD on days 36-63, cyclophosphamide IV over 30-60 minutes on day 36, thioguanine PO on days 36-49, cytarabine IV over 1-30 minutes or SC on days 36-39 and 43-46, and methotrexate IT on days 36 and 43 in the absence of disease progression or unexpected toxicity. 