I was able to fix further problems in the kaffe AWT ilpementation and to integrate it furthermore with classpath. Radiobuttons do work now and menus started to be usable too! Most Layouts seem correct too.
Unfortunately some other compontents (like the tabbed pane) still don't work and I don't know how to solve the problem.
The attached screenshot shows the portability of a swing that uses directly X11: it is running on Irix on a SGI Indigo2.