Arm A - stavudine (d4T)/nevirapine/ritonavir Arm B - d4T/lamivudine (3TC)/nelfinavir Arm C - d4T/nevirapine/nelfinavir Arm D - d4T/3TC/nevirapine/nelfinavir. Prior to randomization to 1 of the PRAM 2 treatment arms, patients are stratified based on their CD4% (less than 25% and greater than or equal to 25%) and by age (less than 24 months and greater than or equal to 24 months). The first 35 subjects/treatment arm are evaluated with special immunologic studies including lymphoproliferative assays and extended panel immunophenotyping. There is an interim analysis after all patients have completed 12 weeks of treatment. Patients are treated for 48 weeks. [AS PER AMENDMENT 6/11/99: The study has been extended for an additional 48 weeks (96 weeks total) to permit long-term follow-up of clinically stable, HIV-infected children.]