I want to make a simple Go board to design an Computer Go game.

In a go game, you lie a "stone" (white or black) on a position where horizontal and vertical lines intersect.

What are some simple ways to restrict users from placing their stones in other locations?
Maybe I'm just not seeing a simple solution.

EDIT
I guess I should rephrase my question better: I want to know how to do the background image of Go board, so that I can lie my stones on the intersection of the horizontal and the vertical lines. I was thinking about getting a just regular Go board image, and when I'm actually rendering stones, I find right position of pixels to lie stones. However, that solution did not seem to be the best solution, since I need to worry about size of stone images and think about proportionality when I either expand or shrink the board window.