To evaluate the safety and tolerance of the combination of adefovir dipivoxil at two comparative doses and nelfinavir plus saquinavir SGC administered orally (Group 1) vs. the combination of adefovir dipivoxil and nelfinavir plus either zidovudine, lamivudine, or stavudine (Group 2) vs. the combination of adefovir dipivoxil and saquinavir SGC plus either zidovudine, lamivudine, or stavudine (Group 3) in HIV-infected patients with prior nucleoside reverse transcriptase inhibitor therapy but no prior exposure to protease inhibitors who have CD4 cell counts >= 100 cells/mm3 and an HIV-1 RNA baseline copy number >= 5000 copies/ml. To determine the proportion of patients whose plasma HIV-1 RNA level falls below the level of detection (<500 copies/ml) at 20 weeks of study therapy and the average reduction in HIV-1 RNA from baseline through study week 20. To evaluate the durability of the antiviral response through 48 weeks of study in patients who continue on study therapy after week 24.