I followed the directions at http://strobist.blogspot.com/2006/07/how-to-diy-10-macro-photo-studio.html.
It was really easy and I made 2 boxes in an evening. The only alterations I made to his instructions, was to the inside. Instead of using white paper, I spray painted it with matte white Krylon. I attempted to use the paper, but I made a mess. I used matte in an attempt to eliminate all shadows. I think it worked well.