 CONSOLIDATION BLOCK 1: Patients receive imatinib mesylate PO QD on days 1-21, methotrexate IT, cytarabine IT, and therapeutic hydrocortisone IT on day 1, high dose methotrexate IV over 24 hours on day 1, vincristine sulfate IV over 1 minute on days 1 and 6, dexamethasone PO BID or IV on days 1-5, cyclophosphamide IV over 30-60 minutes on days 2-4, leucovorin calcium PO or IV on days 3 and 4, high dose cytarabine IV over 3 hours and pegaspargase IV over 1-2 hours on day 5, and filgrastim SC on days 7-11 in the absence of disease progression or unexpected toxicity. 