The goal of this clinical research study is to learn if intensive chemotherapy, combined with imatinib mesylate (Gleevec, STI571) given for 8 courses over 6 months, followed by maintenance imatinib mesylate plus chemotherapy for 2 years, followed by imatinib mesylate indefinitely can improve Philadelphia-positive acute lymphoblastic leukemia. The safety of this treatment will also be studied.