1) A decent sized cardboard box. The one I used was white on the inside to begin with but you could use whatever stricks your fancy. Make sure the box you use will fit your figures including vehicles.
2) Some parchment paper (used to difuse the light)
3) Sharp utility knife
4) Clear tape
5) Can of white spray paint/primer
With my supplies gathered I set out to cut out the 3 openings in the box. The 2 short sides and the top of the box get a good sized opening cut into them. I went with an opening that was roughly 2/3 the size of the area of the box. Basically you want to leave an area around the edges of the cutout area that you can attach the parchment paper to. This 'frame' that you cutout also keeps the box more stable.
Once you have the box cutout on 2 sides and the top you can spray the inside of the box with your white spray paint. This will help insure that the inside of the box maintains a white nonreflective surface. Once the paint has dried you can now cover the openings you cutout in the box with sheets of parchment paper. Make sure you have the parchment paper pulled tight before you tape it down completely.
Now you are ready to take better pictures of your minis, at least I hope so!
I snapped a couple of pictures of my most recent miniature, he is my figure for our Rogue Trader game. Here is a shot of him before the lightbox:
Here is a shot of him after the lightbox:
While the difference is not huge I do like what the lightbox has to offer. Of course I am still learning how to use my digital camera. Expanding our knowledge base while having fun playing with little toy soldiers, what more could we ask for!?!