To compare the time to progression of CMV retinitis between oral ganciclovir and IV ganciclovir during 20 weeks of maintenance treatment. To compare the safety and tolerance of oral ganciclovir with IV ganciclovir therapy during 20 weeks of maintenance treatment. To describe the safety and tolerance of oral ganciclovir treatment when given concurrently with anti-retroviral treatment, e.g. zidovudine or ddI. To describe the survival of people with AIDS and CMV retinitis.