Thanks again for your comments, well, is not difficult to get this weathering effects, but you need patience, time and some paintbrushes and acrilics, what I did with this ship (and the Anakin's starfighter), first: take them appart, the ARC is easier than the jedi starfighter, get disassembled every part (wings, canyons in the wings, cockpit), with the canyons I painted with metalic spray, after is dry, apply a thin layer of black spray paint (I don't have aerograph), when is dryed, scratch very carefully the edges of the weapon with a x-acto knife, you will see the metalic paint under the black, do this to some areas, take many screenshots to the movies to have a better reference, for the wings and the body of the ship, I did a wash, mix black acrilic with a little of dishwasher soap (liquid), let the paint reach the deep surfaces, after that, with a wet fabric swatch or cotton, clean the surfaces of the ship, leaving the paint in the deepest surcafes ( I hope you understand what I'm trying to mean

), for the weathered red paint, I did use sandpaper, to paint the control panels inside the cockpit, you can use a toothpick or a paintbrush 00 (double zero), for metal effects, use dry brush technique with acrilic paint or a metalic ink pen.
This is some of my technique to do the customs, I tryied to explain the best I could, but if you have any question or tip, feel free to ask, you can add my e-mail to your messengers list (Yahoo or MSN Messenger), this weekend I'll be taking pictures to my troopers to show you the custom I did with them.