Raltegravir (MK-0518) is an HIV-1 integrase inhibitor with potent in vitro activity against HIV-1 strains including those resistant to currently available antiretroviral drugs. The purpose of this study is to assess the effectiveness of raltegravir in further reducing viral load in HIV infected patients that have already achieved viral suppression below the level of detection of standard viral load assays when added to antiretroviral therapy (ART).