Arm B: APV plus indinavir (IDV) plus ABC plus EFV plus ADV. Arm C: APV plus nelfinavir (NFV) plus ABC plus EFV plus ADV. Arm D: APV plus placebo (NFV, IDV, or SQVsgc) plus ABC plus EFV plus ADV. All patients receive L-carnitine supplementation. All patients receive clinical physical assessments and laboratory testing during study as follows: Weeks 2, 4, and every 4 weeks thereafter. A primary analysis is performed after the last patient has reached 24 weeks. [AS PER AMENDMENT 3/2/00: At that time, all patients are unblinded to their original treatment assignment.] Patients who experience virologic failure are unblinded and may choose 1 of the following 3 options: Continue study medications open-label, permanently discontinue study medications, or selectively continue study medications [AS PER AMENDMENT 3/2/00: from the arm the patient was originally randomized to] and combine with other approved antiretroviral agents. [AS PER AMENDMENT 3/2/00: For patients adding didanosine (ddI) to their regimens, monitoring for the development of pancreatitis is crucial.] Final evaluations are required for those patients who are off drug during the immediate 8-week period following the last dose of study treatment. Beyond 8 weeks, they are followed for incidence of death, cancer, congenital anomalies, and permanent disabilities. [AS PER AMENDMENT 3/2/00: Gilead Sciences has terminated its U.S. development of ADV for HIV infection. Gilead will continue to supply ADV for patients in ACTG 398 until the study closes. Patients who are receiving ADV at the completion of the study may continue to access ADV through the Expanded Access Program, provided that the physician and patient have determined that continued use of ADV is beneficial.]