Patients are randomized in a 2:1 scheme to 1 of 2 treatment groups. Group 1 receives GW433908 plus abacavir (ABC) plus lamivudine (3TC); Group 2 receives nelfinavir (NFV) plus ABC plus 3TC. Patients undergo safety and efficacy assessments at the Screening Visit, Day 1 (Entry), and Weeks 1, 2, 4, 8, 12, 16, 20, 24, and every 8 weeks thereafter. A follow-up visit is performed 4 weeks after the permanent discontinuation of study drug. Detailed assessments for the development of lipodystrophy/fat redistribution occur at Day 1, Week 24, Week 48, and every 16 weeks thereafter. Patients have examinations and laboratory tests performed at visits.

Inclusion Criteria

Patients may be eligible for this study if they:

• Are at least 13 years old (consent of parent or guardian required 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 (NNRT) or protease inhibitor (PI).
• Have a viral load (amount of HIV in the blood) of 5,000 copies/ml or more, or have a positive result at the screening visit.

Exclusion Criteria

Patients will not be eligible for this study if they:

• Abuse drugs or alcohol in a way that would interfere with the study, in the opinion of the doctor. Patients stable on methadone will be considered for participation.
• 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 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.