Question: I'm sorry if there is not a whole lot of knowledge backing up this question, but I really want/need to be pointed in the right direction:

I want to develop a simulation of vehicle movement in different 3D landscapes with the "camera" and a limited amount of objects moving in this landscape. The creation of new "landscapes" and new camera and object movements, should be as easy as possible...

So what do I need to look into, to achieve this the best solution?
OpenGL, DirectX, XNA, Certain Game Engines?

Again, the needs for the system:
- Movement of camera in a 3D landscape
- Movement of simple objects in this 3D landscape
- Ease of creating new 3D landscapes

(Or to put it simpler: a driving game without the menus, sound, speed meters, user input and stuff :P)

Answer: 
That's a pretty massive task. I suggest you look at existing 3D engine libraries first such as OpenSceneGraph and Irrlicht, you will also need to learn a graphics API to use those technologies (OpenGL, DX), and to top it all off you will a window and interaction libraries (Qt, wxWidgets, etc).

If you want to visualise data and are not concerned will building a standalone app, I suggest you look at a 3D program that can interpret your model data - Blender, Maya, 3ds max, etc.

As a general rule, anything involving 3D graphics is not easy...
You'll want to use a game engine to do this. Game engines typically have all the features you want, including terrain rendering, camera controls, object physics etc.

There are lots of options in the game engine space, I would personally recommend an open source game engine like [jMonkeyEngine](http://jmonkeyengine.com/) (which is built on top of OpenGL and Java). It has lots of good example code you can learn from or build upon and it certainly [has all the features](http://jmonkeyengine.com/engine/) you are likely to need.