The children will either continue to receive the anti-HIV drugs they have been taking, or their medicines will be changed to a different combination of protease inhibitor and reverse transcriptase inhibitor. Before and during the study, patients will undergo various tests, including a physical examination, blood tests and chest X ray, immune response tests, CT scan, eye examination, electrocardiogram and echocardiogram. A procedure called apheresis may be done to collect white blood cells. In this procedure, whole blood is drawn similar to donating blood, the white cells are separated out by a machine, and the red cells are returned to the body.