This study will examine the safety and effectiveness of Zenapax (a laboratory-manufactured antibody) in treating multiple sclerosis. Multiple sclerosis may be caused by an abnormal immune response in which white blood cells called T lymphocytes attack the myelin sheath that covers nerves and parts of the spinal cord. Zenapax binds to protein receptors on lymphocytes, keeping them from interacting with interleukin-2, a substance necessary for their growth.