All of the DS evaluation boards and motherboard designs are license-free and the whole documentation kit for a design costs about \$50. That includes all the schematics, programmable parts sources, data sheets for CPU and support chipset. The doc kits are available from Digital Semiconductor distributors. I'm not suggesting that many people will want to rush out and buy this, but I do want to point out that the information is available.
Hope that was helpful. Comments/updates/suggestions for expansion to Neal Crook.