 - Subjects must be able to receive a RTV-boosted PI as part of their OBT regimen. Due to the possibility of randomization to the placebo arm, investigators should consider subjects for enrollment whose treatment history and resistance testing results suggest that an OBT regimen can be constructed which would be anticipated to provide the best possible virological response and clinical benefit for each subject. The drugs in the OBT regimen will be chosen from the locally available antiretrovirals and must consist of between three and six drugs, one of which must be a RTV-boosted PI. Use of investigational PIs which become available through expanded-access or similar programs during the conduct of this study must be authorized by the Sponsor prior to use in OBT regimen. 