The purpose of this study is to learn how well atazanavir (ATV) works in combination with ritonavir (RTV) or saquinavir (SQV) with tenofovir (TDF) and a nucleoside to reduce the viral load of treatment experienced subjects with human immunodeficiency virus (HIV). There is a comparison arm with lopinavir (LPV)/RTV and TDF and a nucleoside.