To compare the safety and efficacy of antiretroviral therapy (zidovudine plus either didanosine or dideoxycytidine) versus antiretroviral therapy plus intravenous cytarabine (Ara-C) versus antiretroviral therapy plus intrathecal Ara-C in the maintenance or improvement of neurological function over 6 months in HIV-infected individuals who have developed progressive multifocal leukoencephalopathy (PML). To compare the effect of these three treatment regimens on Karnofsky score and MRI studies.