To compare the durability of the viral load response following 48 weeks of treatment with 1592U89/lamivudine (3TC)/zidovudine (ZDV) versus 3TC/ZDV alone. To compare the early antiviral activity following 16 weeks treatment with 1592U89/3TC/ZDV versus 3TC/ZDV alone as demonstrated by the proportion of subjects with viral load < 400 copies/ml, plasma HIV-1 RNA profiles and CD4+ profiles. To assess the safety and tolerance following 16 and 48 weeks of treatment with 1592U89/3TC/ZDV versus 3TC/ZDV alone.