I've been looking in to this a while back.
I have found that there are two supplies of checkering tools:
http://www.gunline.com/index2.html
http://www.dembartco.com/
They come in different sizes, lines per inch. 20 lines per inch is the most common.
I bought the Gunline Camp Perry Set, 20 lines per inch. It is the middle set of the three they offer. I'm very content with it, although checkering takes a LOT of time and is very precise.
The basics are very easy. If you buy a set, it will com with a booklet with instructions, wich will get you going.
http://www.gunline.com/included.html
Basicaly you need fine grained wood to work with.
Draw the outlines of the part you want checkered.
Draw two lines wich will be your masterlines. (I used duckt tape to keep the line straight around the bends)
Very common is a 3:1 ratio. (the checkers will be 3 times higher than they are wide)
Use a single line cutter and cut the two crossing lines. Next you take a two line cutter. The line you just cut will be a guide for the tool and the second line will be exactly parallel to the first.
And so you go on untill you are finished.
At the moment I am checkering the handle of my hammer for practice.
Becouse a hammer handle, just like a knife handle, is rounder than a gun stock it is a bit trickier. I am very happy to have a 3-line cutter, it comes in very handy.
I switch a lot between the 2 line cutter and the 3 line cutter.
Before I started my practice on my hammer I thought that 20 lines per inch would be a bit bulky for a knife handle. But now I think it will be just right.
I wouldn't advice to go any finer than 22 or 24 lines per inch.
I also bought this book:
http://www.amazon.com/Checkering-Ca...2558401?ie=UTF8&s=books&qid=1178363509&sr=8-1
I thought it would be a how-to book. It is not, but is does have a lot of photo's of very beautifull works of checkering. If you need inspiration, the book could be handy, but don't expect it to tell you how to do it.
Hope this helps.