But when I maximize my window it takes the two screens. Is this intended behavior ?It's obviously not intended by you, but it's normal because Big Desktop doesn't provide the Xinerama extension yet.
Where did you find this ? Is there a page that sum up all the problem with the fglrx driver ?
If that doesn't work, your shell startup scripts probably override the DISPLAY environment variable?
...ooops sorry for the noise. I completely forgot about this one. I effectively had DISPLAY=:0.0 in my .zshenv.
Anyway Michel thanks a lot for your help. Mathieu