Treatment Block 1: Patients receive cytarabine intrathecally (IT) on day 1 and methotrexate IT on days 15 and 29. Patients also receive vincristine intravenously (IV) on days 1, 8, 15, and 22; prednisone orally (PO) twice or thrice daily (BID or TID) on days 1-29; pegaspargase intramuscularly (IM) on days 2, 8, 15, and 22; and doxorubicin IV over 15 minutes on day 1. Ph-positive patients also receive imatinib mesylate PO on days 1-14.