 CONSOLIDATION BLOCK 3: Patients receive imatinib mesylate, dexamethasone, etoposide, methotrexate, cytarabine, therapeutic hydrocortisone, pegaspargase, and filgrastim as in Arm A Consolidation Block 3, and high dose cytarabine IV over 3 hours on days 1-2 in the absence of disease progression or unexpected toxicity. 