Study to Explore Safety And Tolerability of Fosamprenavir With or Without Ritonavir in Combination With TRIZIVIR or COMBIVIR

Inclusion Criteria: * Lab result for Screening viral load (HIV-1 RNA) greater than or equal to 1,000 copies per mL. * Lab result for Screening CD4 cell count greater than or equal to 100 cells per microliter. * Antiretroviral therapy naive (no prior therapy allowed). * Male or female 13 years of age or older (or 18 years of age or older according to local requirements). * Female subjects must be of non-child bearing potential (i.e. physiologically incapable of becoming pregnant, including women who are post-menopausal) or of child-bearing potential with a negative blood pregnancy test at screen and who agree to use a proven barrier method of contraception (e.g. spermicide plus condom) during the study period. Hormonal contraceptives will not be considered sufficient forms of contraception for this study. All subjects participating in this study should be counselled on the practice of safe or safer sex. * Able to understand and provide written informed consent to participate in this trial. Parental or guardian consent must also be obtained for subjects under the age of 18 years. Exclusion Criteria: * Prior history of having received antiretroviral therapy. * An active HIV Associated Disease (Center for Disease Control Category C) within 28 days of study drug administration. * Any sudden onset or sharp rise in a laboratory abnormality (including abnormally high laboratory values) at Screening that causes the investigator to have the opinion that the subject should not participate in the study of an investigational compound. * Subjects with a laboratory result for estimated creatinine clearance less than 40 ml per minute within 28 days of study drug administration. * Laboratory result for serum aminotransferase (AST, ALT) levels elevated greater than five to ten times (or more) the upper limit of the normal range within 28 days prior to study drug administration. * Pregnant or lactating women. * History of clinically relevant pancreatitis or hepatitis within 6 months of study drug administration. * Presence of any serious medical condition (e.g., diabetes, cardiac dysfunction, hepatitis) which, in the opinion of the investigator, might compromise the safety of the subject. * Presence of a malabsorption syndrome or other gastrointestinal dysfunction which might interfere with drug absorption or render the subject unable to take oral medication. * History of a drug or other allergy which, in the opinion of the investigator, contraindicates the subject's participation in the study. * Treatment with radiation therapy or cytotoxic chemotherapeutic agents within 28 days of study drug administration or anticipated need for such treatment during the study. * Treatment with immunomodulating agents (such as systemic corticosteroids, interleukins, interferons) or any agent with known anti-HIV activity (such as hydroxyurea or foscarnet) within 28 days of study drug administration. * Treatment with any HIV vaccine within 3 months of study drug administration. * Treatment with other selected medications within 28 days prior to receiving study medication or the anticipated need during the study. * Current alcohol or illicit drug use which, in the opinion of the investigator, may interfere with the subject's ability to comply with the requirements of the study. Note: Subjects stabilized on methadone can be considered for participation. * Treatment with other investigational drugs or therapies within 28 days prior to Day 1, or an anticipated need for such treatment during the study. Treatments available through a Treatment IND or other expanded-access mechanism will be evaluated on a case-by-case basis. * Other inclusion or exclusion criteria to be determined by the investigator and sponsor of the study.