The purpose of this study is to compare virus response to GW433908/ritonavir (RTV) to viral response to nelfinavir (NFV) when used with abacavir (ABC)/lamivudine (3TC) in patients that have not taken antiretroviral (ART) drugs.

Patients are randomized to 1 of 2 treatment arms. One arm is treated with GW433908/RTV plus ABC and 3TC. The other is treated with NFV plus ABC and 3TC. Each group is treated for 48 weeks. The following are compared in the 2 arms: 1) magnitude and durability of antiviral response; 2) safety, tolerance, and antiviral response after 24 and 48 weeks of therapy; 3) time to treatment failure; 4) immunologic response; 5) occurrence of events related to metabolic abnormalities; and 6) development of viral resistance in a subset of patients following treatment. Also studied are: 1) steady-state plasma drug trough concentrations; 2) demographic, virologic, immunologic, pharmacologic, and adherence factors that may be associated with treatment outcome; 3) patient adherence to the drug regimens; 4) study medication utilization; and 5) resource utilization.

• Drug: Ritonavir
• Drug: Abacavir sulfate
• Drug: Nelfinavir mesylate
• Drug: Lamivudine
• Drug: GW433908

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.