Arm I: ZDV plus 3TC Arm II: d4T plus ritonavir Arm III: ZDV plus 3TC plus ritonavir. Prior to randomization to one of the three arms, patients are stratified based on CD4 percents: either less than 15% or greater than or equal to 15%. The first 8 patients randomized to Arms II and III participate in a real-time Phase I pharmacokinetic study (16 patients total). After the first 45 (15 per arm) patients entered are followed for 24 weeks, an interim analysis is done. Patients are treated for 48 weeks [AS PER AMENDMENT 1/5/98: 72 weeks].