If you're good at airbrushing you can do it all with that.
Start with a white base, do your general wood grain pattern with yellow. Come in with some tangerine candy, then rootbeer candy, then over reduced black.
You tighten up the grain as you progress through the colors. Or you can spray your base color for the wood and use a darker color for the grain.
It all depends on what you want. I find this way to look VERY realistic. I recently did a border on a mural and found it hard to tell if it is paint or wood.
You can also check out Fraser's custom paint book.
It explains it in much greater detail, pics help too.
Dirt