Study of Adding Entecavir to Current Lamivudine Therapy in HIV and HBV Co-Infected Patients

* Documented history of co-infection with HIV and HBV * Stable Anti Retroviral Therapy regimen containing lamivudine 150 mg BID for at least 24 weeks prior to enrollment; * Documented HBV viremia on screening and at least at 4 weeks prior to screening * HBe Ag-positive or HBe Ag-negative / anti-HBe-positive * HIV viral load below 400 copies/mL by the Roche Amplicor(TM) 1.5 HIV PCR assay at screening and equally low at least 12 weeks prior to screening * Absence of Co-Infection with hepatitis C virus (HCV) or hepatitis D virus (HDV) * Absence of other forms of liver disease e.g., alcoholic, autoimmune, biliary disease * Less that 1/2 weeks of prior therapy with nucleoside/nucleotide analogue (excluding lamivudine) with activity against HBV (including e.g. famciclovir, tenofovir, ganciclovir, adefovir). No receipt of any of these therapies within 24 weeks prior to randomization into this study.