Hi!
I am a designer for a long time, but unfortunately i havent worked with 3D objects yet and dont know how to start. For the beginning i need to choose a good programm to work in. What would you recommend me?

To get you started with 3D I recommend Google's SketchUp, or Wings3D. Both are free.

I second the recommendation of Wings3D; there is also a free version of Maya, the Personal Learning Edition (PLE).

I can highly recommend the latest verion of Cheetah3D (v4.1 at the moment), which is reasonably priced at $130. It isn't Maya, but it has *almost* all the tools one really needs from Maya for game modeling and basic rendering and animation. It is completely Mac-native, unlike virtually every other 3D package out there, which have been ported and adapted to the Mac in some way. The documentation is a little rough on the edges because it is made by a non-native English speaker, but even that is survivable. He has steadily put out a series of improvements to it over the years, and as of the latest version I've finally been willing to part with Maya and give it a try. So far, so good!

Here are, software 4 free, several programms to work with 3D, from simple to professional. Choose any:-)

Good luck