Not sure if it is good news for you or not but.... I thought I'd let you know.
I know you want to become a great level designer and all that. Well There are hundreds of programs free or not free and you could try any of them. But something just came out today. One program "Unity" became free (it was 200$ minimum before). As i see it, it is the best program for making games and building worlds at the current pace which is free and very very very easy to use. So please have a look at it and try build your own world there:
The LINK: http://unity3d.com/#freeunity
The thing is, u can build something valuable in this program, then u can do it. Also I advise to use Blender (blender.org) for making 3d objects for Unity, because Unity strongly supports Blender files, so exporting and importing would be very easy.
Hopefully I gave u good news.
For me it is good news, because I wanted to work in it too.