The purpose of this study is to see how taking certain anti-HIV drugs affects the way the body metabolizes fat. This study will evaluate patients who are enrolled in CPCRA 058 (the FIRST [Flexible Initial Retrovirus Suppressive Therapies] study) by looking for changes in cholesterol levels, levels of fat in the blood, and body fat distribution. Patients in the FIRST study receive an anti-HIV drug regimen which contains a protease inhibitor (PI), a nonnucleoside reverse transcriptase inhibitor (NNRTI), or both.