I don't know of any easy way to use a single radio button group and spread out the individual buttons both horizontally and vertically in a single grid. You could try modifying the HTML source code for a radio button group in the form's Customize HTML page, or you could create a grid using a custom HTML field and make each square a clickable element. Then you would need jQuery to monitor the click events and update a hidden field with the chosen value. Whatever you decide, it's a lot of custom work.