need help

I want to know how you guys create affects on cars.I need to know how to create a muddy and rusty affect.Any help would be highly appreciated.Thanx.:)

The mud effect is done with airbrush, I don't know about the rusty effect.

The mud can be made from putty and then painted brown, that is what I did with my nissan p/u pictured here,
http://www.jasonpham.com/~jacksoncreation/modelcars/nissan/images/MuddyNissan_4.jpg
http://www.jasonpham.com/~jacksoncreation/modelcars/nissan/images/MuddyNissan_3.jpg
http://www.jasonpham.com/~jacksoncreation/modelcars/nissan/thumbnails/MuddyNissan_1.jpg

as far as the rust look, I have seen it done before. It takes ALOT of patience and a dremel tool, you drill small holes in the plastic and thin out the thickness of it with sand paper and the dremel. It takes a lot of practice to master but it looks amazing when done correctly!!!