HI somedays ago, I thnk bigsofty speak about voxels, I put some free soft, but if you want something easy to use find blender, all we know it's free and really it's easy to use...
I find this video in youtube, excuseme for don't make the video for my self, but I can confirm this works fine, and it's a simple step, only it's apply a modifier to our mesh or meshes...
I think really it's better this video it's real english not like mine :D :P
Another use for this I think can be for make 8 bits stile graphics from a 3D mesh, the cool you can anime anything and anymode in Blender...