To determine the proportion of patients treated with amprenavir, zidovudine (ZDV), stavudine (D4T) and lamivudine (3TC) whose HIV-1 RNA level remains below the level of detection during 96 weeks of therapy. To determine the proportion of patients treated with indinavir (IDV), nevirapine (NVP), 3TC, and d4T whose HIV-1 RNA level decreases and then remains below the level of detection, during the 96-week therapy period. To determine the viral effects, safety, tolerability, and pharmacokinetics of amprenavir in combination with zidovudine, stavudine, and lamivudine. [AS PER AMENDMENT 2/27/98: To determine the proportion of patients with undetectable plasma HIV RNA, by treatment and baseline RNA cohort (either detectable or undetectable). To determine the durability of these regimens by estimating the distribution of time to loss of virologic suppression (or equivalently, time to virologic failure), by treatment and baseline RNA cohort.] This study allows patients who have successfully participated in ACTG 347 or other trials involving amprenavir to continue treatment with amprenavir, ZDV, d4T, and 3TC. Additionally, this study provides patients whose HIV-1 RNA was not reduced to undetectable levels or who had a significant increase in plasma levels ("treatment failures") the opportunity to change to a potentially more active regimen that includes indinavir, nevirapine, lamivudine, and stavudine.