This map editor is impressive and they claim it is the same tool the developers use in order to create levels for Shogun 2. They even claim that it is fairly easy to use for those with little experience with modding or map creation. It has pre-existing custom brush sets, particle effects and a whole slew of options, but it also allows you to bring in your custom ones. Currently they are having problems with 32 bit operating systems, but the editor is specifically designed for 64 bit operating systems and there aren't any known problems with that. There is a lot of information on teh editors, which I will link to below, but take a look at this episode of Rally Point and see the editor in action.
Total War Forum Post Info on TEd
Total War Forum FAQ for TEd
-Written by Sean Cargle