 MAINTENANCE: Patients receive imatinib mesylate PO QD on days 1-84, vincristine sulfate IV over 1 minute on days 1, 29, and 57, prednisolone PO BID or methylprednisolone IV for course 1 and 2 on days 1-5, 29-33, and 57-61, mercaptopurine PO on days 1-84, methotrexate PO QW, and methotrexate IT on day 1 and day 29 for course 1 and 2. Courses repeat every 84 days for up to 104 weeks from the start of Induction IA in the absence of disease progression or unexpected toxicity. 