The RPG I mentioned, is using the AD&D game system. Basically, I'm connecting the PC's in some way to the main characters. The premise of the world is the same as at the beginning of the book. A game with only the information of the world provided in AGoT, would not work with this game system, so it starts slightly modified and will probably end up greatly modified.
With no more information about the world than one novel to work with -- which masterfully centers on great character development, and leaves fantastical elements at a bare minimum (such as it should be in a great fantasy novel IMO)-- there is just not much to work with for a traditionally high fantasy game syste.
So I'm simply implementing many of the features of the game, the plot (as backdrop at first) the characters (since they are already well developed), the history (as we know it), and the political intrigues.
Expectations are why games based on other mediums, fail as games, IMO. Star Wars, Babylon 5, Dragonlance, are all based on great film, television, and literary endeavors. I have yet to see a RPG that can be worked properly with these. So basically I use it as a backdrop.
Its sounds like lots of fun. Again, for more information, you can e-mail the creator of the rpg, James Todd Twilley, at firstname.lastname@example.org