If you need to take a bitmapped image (like a logo) and turn it into vector art, check out the online app Vector Magic. I have tested it and it is amazing. Here is a rasterized logo (left) and the vectorize result (right). This very easy-to-use web app allows you to render your file low, medium, or high. Then you may download the vectorized file as an editable .eps file or a PNG. It works with photos as well, as you can see on their sample page.
This site is the result of a Stanford University Artificial Intelligence Laboratory research project.
