Peripheral Artery Disease involves a buildup of fatty deposits (plaque) within blood vessels that can restrict blood flow. Patients who have PAD and claudication (pain in legs during exercise due to poor blood circulation) may be eligible for this clinical trial. Three primary hypotheses will be tested in this study: (1) IVUS (Intravascular Ultrasound)combined with advanced digital image and signal processing provides a sensitive method to determine plaque geometry and composition in the human peripheral artery wall; (2) IVUS can discern specific arterial wall morphology, providing data that can be used to identify plaques that predispose the patient to late complications; and (3) IVUS-derived plaque structure can be used to predict responders and non-responders to pharmacologic therapy and percutaneous endovascular interventions. These hypotheses will be tested as follows: (1) custom engineered IVUS analysis software will be used to describe the geometry, composition, and spatial component relationships of the vessel, (2) the morphology of lower extremity arterial plaque, as determined by IVUS, will be correlated with baseline clinical characteristics of subjects, and (3) the effects on plaque morphology after long term treatment with antihyperlipidemics will be determined.