The easiest way is to buy some expensive program or plugin to convert the art for you If you have Flash, that has a way of converting images into vector drawings, but it's not very good. Nor is any other automated method. Really, if you want it to look good, you'd have to trace it manually.
i like the live trace tool in illustrator CS2 .. anyways, but itz not quite clean... other way is to make it step by step in illustrator..