Arm A (control arm): APV and EFV alone. Arm B: APV and EFV plus IDV [AS PER AMENDMENT 12/4/00: APV and EFV plus NFV]. Arm C: APV and EFV plus NFV [AS PER AMENDMENT 12/4/00: APV and EFV plus IDV]. Arm D: APV and EFV plus RTV sgc. Arm E: APV and EFV plus SQV sgc. On Day 14, 15, or 16, volunteers return to the clinic for PK testing following the dual-drug regimen, and again on Day 29, 30, or 31 following the triple-drug regimen (or continued dual-drug regimen for Arm A). [AS PER AMENDMENT 12/4/00: Volunteers attend clinics for PK testing on Days 0 and 1 (first visit), after taking the dual-drug regimen for at least 3 days (second visit, e.g., on Day 14 or after), and after taking the triple-drug regimen (or, if in Arm A, after continuing on the dual-drug regimen) for at least 7 days (third visit).] Before each PK testing, volunteers complete an Adherence Questionnaire. [AS PER AMENDMENT 12/4/00: The Adherence Questionnaire is administered at the second and third PK visits.] Volunteers maintain a food diary. Two to three weeks after completing the drug regimen [AS PER AMENDMENT 12/4/00: Within 2-3 weeks after the third PK visit], volunteers return to the clinic for evaluations and urine and blood sampling.