Comparison of GW433908/Ritonavir to Nelfinavir When Used With Abacavir and Lamivudine in Patients That Have Not Taken Antiretroviral Drugs

Inclusion Criteria Patients may be eligible for this study if they: * Are at least 13 years old (consent of parent or guardian needed if under 18). * Agree to use a proven barrier method of birth control (e.g., spermicide plus condom) during the study period (hormonal birth control will not be accepted), if able to have children. * Have received less than 4 weeks treatment with any nucleoside reverse transcriptase inhibitor (NRTI) and have never received any nonnucleoside reverse transcriptase inhibitor (NNRTI) or protease inhibitor (PI). Mothers who have previously received 1 dose of the NNRTI nevirapine during pregnancy for prevention of mother-to-child HIV transmission are permitted to enter the study. * Have a viral load (amount of HIV in the blood) of 1,000 copies/ml or more. Exclusion Criteria Patients will not be eligible for this study if they: * Abuse drugs or alcohol in a way that would interfere with study requirements. Patients who are stable on methadone will be considered for the study. * Have an active/acute CDC Category C event. * Are unable to absorb or take medicines by mouth. * Are pregnant or breast-feeding. * Have a serious medical condition (such as diabetes, heart problem, hepatitis) that might affect the safety of the patient. * Have had pancreatitis or hepatitis within the last 6 months. * Have been treated with radiation or chemotherapy within 28 days before the study drug will be taken, or will have the need for these during the study. * Have taken drugs that affect the immune system (such as corticosteroids, interleukins, interferons) or that have anti-HIV activity (such as hydroxyurea or foscarnet) within 28 days before the study drug will be taken. * Have received an HIV vaccine within 3 months before the study drug will be taken. * Have received certain other drugs within 28 days before the study drug will be taken, or think that they will be needed during the study. * Have received experimental treatments. * Have allergies which might interfere with the study, in the opinion of the doctor.