A Study to Compare Two Anti-HIV Drug Combinations That Include Amprenavir in HIV-Infected Patients Who Have Failed Anti-HIV Drug Combinations That Did Not Include Amprenavir

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.