To compare the safety, tolerance, durability of the viral load response and the antiviral activity of the 1592U89/zidovudine(ZDV)/lamivudine (3TC) regimen vs. ZDV/3TC regimen. To determine the clinical efficacy of the two regimens as measured survival, disease progression, weight growth velocity, and neuropsychological or neurological changes. To assess the development of viral resistance and relative pharmacokinetics associated with each regimen.