To compare the time to confirmed virologic failure (2 consecutive plasma HIV-RNA concentrations of 500 copies/ml or more) between the treatment arms: abacavir (ABC) or placebo in combination with zidovudine (ZDV), lamivudine (3TC), and indinavir (IDV). To evaluate the safety and tolerability of these treatment arms. [AS PER AMENDMENT 06/16/99: To compare the time to confirmed treatment failure, permanent discontinuation of treatment, or death between the treatment arms.] [AS PER AMENDMENT 12/27/01: Groups B, C, and D completed follow-up on March 4, 1999. Therefore, only information pertinent to Group A is applicable.]