I used fireworks. Someone posted a Photoshop tutorial a while ago but I thought it was kind dumb.
What I did in fireworks was outline the various aspects of the car with a black outline from the pen tool, then fill them with gradients and such to best match the paint job and shadows of the real one.
This is a screenshot I took a while ago, it may help...a bit

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![[Image: attachment.php?pid=363357]](http://shoutbox.menthix.net/attachment.php?pid=363357)
(Click to Enlarge)