Yes, Dawn of Fantasy will ship with a fully-developer- supported Editor (a feature rarely seen). We take utmost case and pride with our editor and can`t wait to share it`s power with future DoF players.
DoF editor, just like WC3 and SC editors fully support GUI scripting. We plan to add really easy to use trigger system as well.
And as far as Editor for Xbox goes, it`s possible to make one, but list of limitation would just be waaay too large and controls too clumsy. However, we do hope to be able to offer our Xbox players easy access to maps made by PC players.