The art folder is usually made when you extract the models and art from the truck pod. There is no models or art or truck files on the hard drive until you extract what you want to work with. For beginners, that's usually from the truck2.pod but if you are attempting to work on a custom that's already made, then you would extract that instead, but the process is exactly the same in both cases. First you extract the files, then you work with them.
If you haven't done the repaint tutorial, then give it a try. It's time well spent.
http://mtm2.com/~mtmg/repaint/
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