Patients are equally randomized to one of two treatment arms. In one arm, approximately 330 patients receive ABT-378/ritonavir plus nelfinavir placebo. In the other arm, approximately 330 patients receive nelfinavir plus ABT-378/ritonavir placebo. In both arms, these protease inhibitors are blinded to the investigator, patient, and sponsor. Both arms receive open-label stavudine and lamivudine. Vital sign measurements, physical examinations, ECGs, routine clinical laboratory evaluations, and determinations of antiviral and immunologic activity are performed at intervals throughout the study.