This is a two part study (Part A and Part B) that will first aim to establish the PK/PD relationship between exposure and lipid effects (Part A: 75 subjects), and will then confirm the effect using the most relevant dose(s) (Part B: ~90 subjects). Doses of 5mg, 50mg and 150mg of GSK256073 will be administered in Part A, and the dose(s) for Part B will be based on the PK/PD data from Part A. Data from Part A and Part B will be combined to decrease overall subject numbers needed in part B. Part B of the study will include a niaspan arm for relative comparison of the effects of GSK256073 and niacin on lipids and flushing