 Patients receive ifosfamide IV over 2 hours and etoposide IV over 1 hour on days 3-5, rituximab IV on days 1 and 3, and carboplatin IV over 1 hour on day 3. Patients receive filgrastim G-CSF subcutaneously once daily beginning on day 6 and continuing until blood counts recover. Patients also receive intrathecal IT chemotherapy comprising methotrexate and cytarabine. Patients with B-cell large cell lymphoma and negative CSF cytology receive IT chemotherapy on day 3 of the first course only. Patients with small non-cleaved cell lymphoma or B-cell acute lymphoblastic leukemia and negative CSF cytology receive IT chemotherapy on day 3. All patients with positive CSF cytology receive IT chemotherapy on days 3, 10, and 17 of the first and second courses. Treatment repeats every 23 days for up to 3 courses in the absence of disease progression or unacceptable toxicity. 