CMV infection, most commonly of the retina (also known as CMV retinitis), is a common OI observed in HIV patients. Despite treatment, CMV retinitis can result in severe visual impairment and CMV disease is associated with reduced survival time. HIV patients receiving highly active antiretroviral therapy (HAART) for HIV infection who have CD4 counts less than 100 cells/mm3 may be at increased risk of CMV infection and its complications. Valganciclovir was approved by the FDA on March 29, 2001 for treatment of the symptoms of CMV retinitis in patients with weakened immune systems, including people with HIV and AIDS. This study will evaluate the safety and efficacy of valganciclovir in preventing CMV organ damage in HIV patients.