HTML Preview works as I mentioned above, but this is not sufficient for me, because PDF generation must work, too (and it does not work :( ).
I didn't find helpful resources on cvc for version 6.x, but I hope the wiki-documentation will give useful hints (it's still in progress).
I found some more information here (http://community.jaspersoft.com/wiki/custom-visualization-component-jaspersoft-studio-v56x), but I don't know if it's still up to date (Version 5.6).
The best resource seems to be the source code of the examples :).
Let's hope for further help of the community :)