How-to for version 0.0.5
OLD how-to for version 0.0.1 here

This software was created using C++ with the Microsoft VC++ 2010 runtime (x86), OpenGL 3 and Microsoft .Net 4.
You may need to install the respective runtimes and a graphics driver. You also need to know whether you have an NVIDIA or an ATI graphics system.

I have tested this with vanilla Minecraft 1.7.4 and also Minecraft 1.4.6 + Buildcraft 3.X + Redpower 2.X + Industrialcraft 2.X. It worked well :)

Let's set up the editor first.
After unzipping, you are presented with a folder that contains no .exe file yet! But there is a "First start and tasty fresh cookies!.bat". Run that one first.
It tells you some things and then asks you to press any key.
Before you do that (before you press any key), go back to the directory and run one of the two files marked here that correspond with your graphics system. I have an NVIDIA graphics card in my computer, so I run the NVIDIA batch file. It just creates a "workaround marker file" to tell the editor to behave in certain ways tailored for that graphics system.

Once that's done, hit any key in the still open cookie window and watch the editor compile its plugins.

Press any key again to delete that setup script and receive your well-earned editor executable file.
The editor, as you run it, should be a gray window with a main menu in it.
You can press F12 to toggle the main menu that is displayed.

Let's make a little test world in a Minecraft version of your choice next.

In the editor, click on "Open world" and select the level.dat file in the folder of your Minecraft world.

A 3D view will appear.
In Version 0.0.5 of the editor, there are no contents displayed yet in the 3D views! I am still working on that!
Bring up the "World manipulations" plugin and set the bounds to an area that you've scouted in Minecraft using the F3 debug mode there.
In this example, I've set the bounds and then used the function "Make a desert".
Note: There is no notification when the action finished, other than that the start button is not highlighted anymore when you moved the mouse somewhere else.

Now close the world in the editor by closing the 3D view, and open the world in Minecraft again.
This is my result.

Please note something very important: The open views correspond to opened Minecraft worlds.
A Minecraft world can be open either in Minecraft or in the editor, but not in both at the same time.
So make sure to exit a world in Minecraft before editing it, and to close all the open views in the editor before opening the respective world in Minecraft again.

If you have multiple worlds open in the editor, the world of which a view is currently selected will be the target of the plugins.
You can tell which view is selected by looking at the top left corner:

So, well. I hope this helps you get started!
Stay tuned for more to come, and feel free to snoop around in the files of the editor - You can configure and change a lot there. :)
Design by Hai.