This 48-week study consists of two steps. In Step 1, patients will begin a lipid-lowering diet and exercise regimen that will continue throughout the study. After 4 weeks on the regimen, patients will enter Step 2 of the study and will begin extended-release niacin therapy. During Step 2, niacin will be dose-escalated every 4 to 6 weeks over a 16-week period. At Weeks 14 and 20, the niacin dose will be determined by blood fat levels. Patients will remain on the dose set at Week 20 for the remainder for the study. If blood tests taken at Week 24 show that blood fat levels have not improved significantly, patients have the option of adding another fat-lowering drug to their therapy.