@phector2004: You are completely free to use our (Radiant’s) stuff, with one caveat. That is, you can use any item that is in the game, or any playable feature – but we ask that you not modify or otherwise use unreleased features or content. We know that in some cases code for an unreleased feature may be present in a given release, though in a dormant state. Please wait until something is official and playable before, um, playing with it.
You don’t need to ask us for permission to use our stuff… but we’d appreciate a credit when you let your creation loose upon the world.