Atazanavir Versus Lopinavir/Ritonavir (LPV/RTV) in Patients Who Have Not Had Success With Protease Inhibitor-Containing HAART Regimen(s)

Inclusion Criteria Patients may be eligible for this study if they: * Are receiving a PI-containing highly active antiretroviral therapy (HAART) for at least 12 weeks. * Have a viral load of 1,000 or more copies/ml within 4 weeks of screening and within 4 weeks prior to randomization. * Have 2 CD4 cell counts of 50 or more cells/mm3 at least 96 hours apart and within 4 weeks before randomization. * Are at least 16 years old. * Have a documented virologic response to at least 1 HAART regimen. * Have phenotypic sensitivity to at least 2 of the following: ddl, d4T, ZDV, 3TC, ABC. * Have phenotypic sensitivity to atazanavir and LPV/RTV. * Use effective barrier methods of birth control. * Will be available for 48 weeks. Exclusion Criteria Patients will not be eligible for this study if they: * Have taken 2 or more PIs and had virologic failure. * Have taken atazanavir or LPV/RTV. * Have an HIV-related infection (within 30 days) or any medical condition requiring treatment at the time of enrollment. * Have had acute hepatitis in the 30 days prior to study entry. * Have received certain drugs within 3 months of study start or expect to need them at time of enrollment. * Abuse alcohol or drugs in a way that would interfere with the study. * Have very bad diarrhea within 30 days prior to study entry. * Are pregnant or breast-feeding. * Have a history of hemophilia. * Use lipid-lowering drugs (within the previous 30 days). * Have cardiomyopathy or symptoms of other heart disease. * Cannot take medicine by mouth. * Have any other condition that would interfere with the study. * Have pancreatitis, if choosing ddI as part of NRTI pair. * Have bilateral peripheral neuropathy at time of screening, if choosing ddI or or d4T as part of the NRTI pair.