Patients will be randomized to receive either a standard dose of LPV/r (Arm A) or a concentration-adjusted dose of LPV/r (Arm B). Concentration-adjusted dosing means that the dose of ritonavir or lopinavir may be increased based on the amount of lopinavir measured in the blood and the results of a drug resistance test. All patients start the study taking LPV/r, tenofovir disoproxil fumarate (TDF), 0 to 2 additional nucleoside reverse transcriptase inhibitors (NRTIs), and saquinavir (SQV) or amprenavir (APV). Only LPV/r, TDF, and SQV will be provided by the study. Other medications taken as part of the antiretroviral regimen must be obtained outside the study.