The objectives of this study are: 1. To evaluate the safety and antiviral activity of monotherapy with ABT-538 at a dose of 600 mg BID, monotherapy with AZT at a dose of 200mg TID and a combination therapy with ABT-538 and AZT in HIV infected patients; 2. To study emergence of resistance to ABT-538. All patients participating in this trial will be allowed to cross over to the ABT-538 arm of the trial and will be continued to be monitored for virological data.