There is a modding document that explains all the whats and hows of modding. It comes with the full Version of the game. I'm not sure if it is included in the demo Version, but I would be surprised. There is also a tile editor and other tools that come with the full Version.
btw: What do you mean when you say you can't find it on the net? Just go to the shrapnel Dungeon Odyssey page and click on the 'order' link. They ship all over the world.
Cheers!
