Rosiglitazone and glyburide are two commonly used diabetic medications that have both been shown to be effective in controlling blood glucose levels. Since they work in different ways, they may have different effects on the health of the blood vessels. This study will assess which medication is better at improving the health of the arteries separate from the blood glucose lowering effects. Artery health will be assessed non-invasively by ultrasound. Certain markers of atherosclerosis found in the blood will also be measured.