Many patients who take 3 anti-HIV drugs together are able to achieve very low viral loads, for example, viral loads below 50 copies/ml. However, some patients taking only 3 drugs are not able to achieve a viral load this low. Doctors hope that, by adding the drug ABC to a current treatment, a viral load below 50 copies/ml can be achieved. Doctors would like to find out if it is effective to start patients on 3 drugs and then add another drug (treatment intensification) if the treatment is not working as well as hoped.