 CONSOLIDATION BLOCK 1: Patients receive imatinib mesylate, methotrexate, cytarabine, therapeutic hydrocortisone, high dose methotrexate, vincristine sulfate, dexamethasone, leucovorin calcium, high dose cytarabine, and pegaspargase as in Arm A Consolidation Block 1, and filgrastim SC on day 7 in the absence of disease progression or unexpected toxicity. 