AR therapy is rapidly becoming the standard of care for the treatment of HIV infection. AR therapy provides the best opportunity for maximizing viral suppression, reducing toxicity and delaying the emergence of resistant strains. The newest class of AR agents, the HIV protease inhibitors, exhibits the most potent anti-HIV effects described to date. This study will compare 2 protease inhibitors, NFV and RTV for efficacy and safety in a population with advanced HIV disease, who are taking various background nucleoside therapies.