 INTERIM MAINTENANCE WITH CAPIZZI METHOTREXATE: Patients receive imatinib mesylate PO QD on days 1-56, vincristine sulfate IV over 1 minute and methotrexate IV over 2-15 minutes on days 1, 11, 21, 31, and 41, methotrexate IT on days 1 and 31, and pegaspargase IV over 1-2 hours on days 2 and 22 in the absence of disease progression or unexpected toxicity. 