Patients continue to receive their ACTG 375 antiretroviral therapy until they register to A5136. Following entry evaluations, patients replace the protease inhibitors (PIs) in their ACTG 375 regimen with lopinavir/ritonavir (LPV/r), add tenofovir disoproxil fumarate (TDF) to their regimen, and maintain the rest of their ACTG 375 regimen for 48 weeks. Patients have clinic visits at entry and at Weeks 4, 12, and 16. After 24 weeks, patients have clinic visits every 12 weeks. Blood is drawn at these visits for viral load, immune response, and other routine tests. A skin test, a urine sample collection, and a pregnancy test (for women of reproductive potential) are also performed at entry. Patients also receive immunizations. At Weeks 12 and 16, a lyme vaccine, polyvalent is administered. At Week 36, lyme vaccine, polyvalent; pneumococcal vaccine, polyvalent; and haemophilus b conjugate (HIB) vaccine are administered [AS PER AMENDMENT 05/14/02: Lyme disease vaccine has been removed from the study due to unavailability]. At Week 48, skin tests are performed. Week 52 is the final clinic visit, at which blood is drawn and a urine sample is taken.