dragging objects horizontally in a grid or in increments

Hi Just to clarify.. I am a complete rookie at programming. I want to make a simple puzzle. For this I need the player to be able to click and drag a gameobject horizontally. It is important that the gameobject (which is a cube in this case) moves in a grid.. or in increments so it seems like a grid. I found the script below... however I cant seem to get it to move in increments. How should I go about doing this? Pseudo-code or actual code will be greatly appreciated!

http://www.unifycommunity.com/wiki/index.php?title=DragObject

Really no one? Hmm