see creating a custom shape file here
MicroCFD - Virtual Wind Tunnel Tutorial
To get a list of points for a car image you can flip a BMP upside down and load it into M$ paint. M$ paint allows you see coords of where your cursor is over an image from a point in the upper left corner (this is why I told you to flip your picture upside down). From there just move your cursor over each corner and along points on each curve to get your list.