Hey thanks everyone for your replies!
I should have been clearer... I've been a mapper/level designer, non-professionally, since 1999 or so. UnrealED. TESCS, Deathmatch Maker - recently Sandbox and DeleD. I know all about what needs to be in an editor, how it should be designed, the features it shoudl have, and what I want to do. I haven't sat down and sketched everything out, but I have what to build covered.
What I do not have completely covered is how to build, hence this thread. In fact, I am not intending to begin building one for a little while as I wrap up getting intimtaely famillair with C++, OpenGL, DirectX and Windows Programming. Probably have to through WPF in there. I have the basics of programming down, but am not past the stage of very basic appliations. I have about a half dozen books to go through and some source code to study before I'm ready.
The whole point here is to have something to look forward to, a goal, something to aim for. You would have to know a little about me and my situation to completely understand this. Essentially I am looking ahead with some idea of what I would like to first begin building, once I have the ability to. I thought I would start looking and requesting tutorials early, so that when I was ready I would have the material I needed.
What I want to do is to build a very basic editor for Myst Online Uru Live. Currently the game is pretty much dead, and part of the reason why, outside its age, is that it is too hard and complex for the community to create and share ages. I would like to address that. Make a very easy to use tool, also very basic, that allows the import of models and a sort of "put the pieces together" design element like TESCS. No terrain or AI or fancy stuff yet. Just the ability to build an age using current or custom meshes, make a book for it, and have it all be as easy to do as possible. As my skills develop I may add more features, or I may even work on the game code.
At some point I would like to include Wings 3D within it for modeling, or make it work as seamlessley with Wings 3D as possible. Why not Blender? Because I can make something in Max or Wings 3D that would take me a few hours in Blender. Blender is too slow, too complicated, and too poorly designed. My apologies to any Blender fans offended. Wings 3D is the best Open Source/Free editor alternative I have found to date.
Interface design and documentation are my specialities. I know what I build will be very easy to understand and use. But developing this editor for Uru is just one step towards my eventual goal of making my own game engine and toolset.
So that's the plan. If you find a good tutorial, or heck, even a decent book, please let me know about it. Thanks!