I know there are the contrib, incubator, trac and so on.
But I’d like to help out with some improvements directly! For example
this ticked i created
and others would be easy to do even I don’t understand the whole vaadin.
Should I copy the whole Window-Class to the contrib, with the added method and you will integrate it in vaadin? Or is there a way to join your team?
Greez
Michel, I suppose you can just fix(work on) tickets and then submit a patch that will be included by the main tree by one of Vaadin comitters.
This is correct. You can submit a patch and it will then be reviewed by someone from the R&D team. If the patch is ok, then it will be merged into the repository. And I do have to mention, we are more than happy to get patches from the community!
Ok. Can you please describe the “submit a patch” part more precisely? 
I just checked out the source, changed a file and selected “create patch”… and then?
You should be able to attach the file to the ticket, that way its easy to find along with what it fixes.
Very nice of you to contribute!
We have a page in trac wiki:
http://dev.vaadin.com/wiki/CreatingPatch
Then attach the file to trac ticket as suggested.
ok I did my first little contribution
Two more question:
At the moment, you don’t use parameterized types (e.g. Iterator). In trac I read it’s ok now to use Java 5/6, so that means you’re going to change this?
Is it ok to accept any tickets I’d like to do? Or should i just add a comment and provide the patch?
Part of the code has been converted to use parametrized types internally but most of the public API still does not use them (some exceptions like the BeanItemContainer exist). At the moment we continue to gradually convert to parameterized types alongside other tasks. Note however that we use Java5, not Java6, so avoid Java6 specific code.
If you are working on a ticket, please accept it so everybody knows. It is also fine to just add a comment and provide a patch, especially for smaller, simpler tickets.