Determination of clinical, lipid, and non-lipid risk factors has been the traditional approach for gauging an individual's risk for coronary artery disease (CAD). However, the IMT test, which uses sound waves to measure the thickness of the carotid artery, has been found to diagnose CAD and predict a person's risk for heart disease as well as or better than lipid and non-lipid risk factors. This study will use the IMT test to see if anti-HIV treatment and HIV infection affect a patient's risk of developing atherosclerosis (hardening of the arteries) by comparing carotid artery thickness among HIV infected adults taking PIs, HIV infected adults not taking PIs, and HIV uninfected adults.