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