Here is a good tutorial from the Forza.com forums on creating detailed graphics. Its very helpful.
http://forums.forzamotorsport.net/forums/thread/214564.aspx
And also here is a good FAQ on painting.
Also, here is a four-part tutorial: http://www.youtube.com/watch?v=dwTZ8NpBGtY&mode=related&search=
Livery Editor Shortcuts & Tips in the Turn 10 Blog.
FAQ on Painting:
Can you import pictures?
No. As photorealistic as these images have gotten, there is no way to import pictures from a PC whether it be Windows, Macintosh, Linux, Free BSD, Oracle, Unix, or any other obscure operating system you may have. There are rumors of “hacked systems” which may or may not be true, but give all designers found in our forums the benefit of the doubt.
How do I copy the left/right side?
When you have completed one side of the vehicle, go to the opposite side and press A. The second button from the bottom is “Insert all from Left/Right”
How do I copy a design from one car to another?
To copy a design from your vehicle to another of the same make and model go to the “Save Design” option in the “Paint Car” menu. The second option is “Save to Design Catalog.” To apply your design, go to the “Design Catalog” option in the “Paint Car” menu and you can see any designs saved to the catalog and select the appropriate design.
How do I get a picture on more than one car/on another side of the vehicle?
To apply a picture from one car to another (or one side of a design), click and hold down the left stick of the controller and press A to highlight the desired layers. Once this is done select the highlighted layers by pressing A, and the third option from the top is “Create New Vinyl Group” Select this and you can name and save your image. Now, go to the desired side of the vehicle (or go get your other car and return to the Livery Editor) and press A. The third option from the top is “Load a Vinyl Group” where you should see any groups you have saved.
How do you make these images from shapes?
For detailed instructions please see ONI 23’s picture tutorial in this forum.
Or Neuborn's step-by-step car from concept art to a finished face in this forum.
How do you paint rims?
In order to paint rims, you must have purchased custom rims. Once this is done you will see a "Paint Rims" option in the paint menu.
This FAQ was not my work it can be found here:
Original Source
Edited 8-14-2007 by Snowowl to add another tutorial link.