The purpose of this research study is to test the safety and effectiveness of ABT378/ritonavir in combination with two nucleoside reverse transcriptase inhibitors and Viramune (nevirapine) in HIV-infected adults who are 1)currently receiving antiviral therapy with a regimen that includes a protease inhibitor and one or two nucleoside reverse transcriptase inhibitors and 2)have a viral load between 1000 and 100000 copies/mL.