Arm B: ddI, d4T, EFV placebo, and NFV. Arm C: lamivudine (3TC)/zidovudine (ZDV), EFV, and NFV placebo. Arm D: 3TC/ZDV, EFV placebo, and NFV. Arm E: ddI, d4T, EFV, and NFV. Arm F: 3TC/ZDV, EFV, and NFV. Patients with virologic failure on 2 successive measurements or study-drug intolerance discontinue their randomized study therapy and proceed to Step 2. [AS PER AMENDMENT 7/5/00: Patients must switch regimens as soon as possible after confirmation of virologic failure to prevent development of drug resistance.]