Participation in this study will last 4 weeks. All participants will undergo initial assessments that will include various vascular and metabolic evaluations. Body weight, height, basal heart rate, and systolic and diastolic blood pressure will also be measured. Participants will then be assigned randomly to receive 4 weeks of treatment with 400 mg of atazanavir per day plus placebo, 400 mg/100 mg of lopinavir/ritonavir twice per day plus placebo, or placebos for both drugs per day. Upon completing the 4 weeks of treatment, participants will repeat the initial assessments.