A Study to Compare Two Anti-HIV Drug Combinations in HIV-Infected Patients Who Have Previously Received Anti-HIV Treatment

Inclusion Criteria Patients may be eligible for this study if they: * Are at least 12 years old. * Are HIV-positive and have a viral load (level of HIV in the blood) of 1,000 - 100,000 copies/ml. * Are currently taking an anti-HIV drug combination that includes 1 PI and 2 NRTIs, and that has not been changed in at least 12 weeks. * Are naive to (have never taken) at least 1 NRTI, other than zalcitabine or abacavir. * Agree to abstinence or use of an effective barrier method (e.g., condom) of birth control. Exclusion Criteria Patients will not be eligible for this study if they: * Have an active illness. * Have received treatment for any active opportunistic (AIDS-related) infection within 30 days of study entry. * Have ever received a nonnucleoside reverse transcriptase inhibitor (NNRTI). * Have received investigational (not yet approved by the FDA) drugs within 30 days of study entry. * Have received treatment with a PI other than their current PI. * Are receiving chemotherapy for cancer. * Are pregnant or breast-feeding.