This study will compare the safety and effectiveness of two anti-HIV drug combinations in fighting HIV infection in patients whose viral loads (levels of HIV in the blood) rose with other anti-HIV drug treatments.

Patients experiencing virologic failure while receiving an IDV-containing antiretroviral regimen will receive the 3TC/ABC/APV/NFV combination. Patients experiencing virologic failure while receiving an NFV-containing antiretroviral regimen will receive the 3TC/ABC/APV/IDV combination.

Inclusion Criteria

You may be eligible for this trial if you:

• Are HIV-positive.
• Are 13 years of age or older.
• Are currently taking anti-HIV drugs, 1 of which must be NFV or IDV, and have taken these same drugs for at least 12 weeks.
• In the last 16 weeks your viral load (level of HIV in the blood) dropped below 400 copies/ml and has since increased to at least 1,000 copies/ml, even though you continue to take your anti-HIV drugs.
• Have the written consent of a parent or legal guardian if you are under age 18.
• Agree to practice abstinence or use effective barrier methods of birth control (unless you are physically incapable of becoming pregnant).
• Are willing to complete the 48-week study.

Exclusion Criteria

You will not be eligible for this trial if you:

• Have ever taken the following anti-HIV drugs: ABC, APV, efavirenz (EFV), delavirdine (DLV), nevirapine (NVP), or loviride.
• Have certain AIDS-related infections or diseases, have other serious medical conditions such as diabetes and certain types of heart trouble, or have a history of lymphoma.
• Have had certain types of hepatitis in the past 6 months.
• Have received an HIV vaccine in the past 3 months or a flu vaccine in the past 30 days.
• Have certain digestion problems that make it difficult to take anti-HIV drugs by mouth.
• Have received certain other drugs or treatments in the past 30 days, or will need certain drugs or treatments during the study.