Patients are randomized to receive either adefovir dipivoxil or placebo daily for 24 weeks, after which all patients will receive open-label drug for an additional 24 weeks. Study drug is administered in combination with a current antiretroviral regimen for the entire 48 weeks. Patients are followed every 4 weeks during the first 24 weeks of study, then every 8 weeks during the last 24 weeks.