Preventing Cytomegalovirus (CMV) Organ Damage With Valganciclovir in People With HIV

Note: Per a recommendation from NIAID Therapeutic Trials Data Safety Monitoring Board (DSMB), this trial will close on 10/03/05. The DSMB has determined that the study will reach the primary objective. All participants not on valganciclovir must complete all study evaluations by 08/31/05; all participants taking valganciclovir must complete study evaluations by 10/03/05. Inclusion Criteria for Step 1: * HIV infected * Viral load greater than 400 copies/ml * CD4 count less than 100 cells/mm3 * Have taken HAART for 3 months or longer OR are not taking HAART and do not plan to start HAART for at least 3 months after study entry * Have serum CMV IgG antibodies * Have consent of parent or guardian if under 18 years of age * Willing to use acceptable forms of contraception Exclusion Criteria for Step 1: * History of CMV end-organ disease * Certain antiviral drugs for CMV prophylaxis within 8 weeks of study entry * Pregnant or breastfeeding * Currently require ongoing foscarnet or cidofovir. Limited courses of foscarnet or cidofovir for the treatment of diseases other than CMV are permitted if approved by the protocol chairs.