Hello,
thank you very much for the great answer found here :-)
I have compiled sawfish, I have to find out how to only use one of my screen, and I have also to find out how to have borderless windows...
Right now, I really dislike the look it has by default, but I could certainly change this...
The best would be with ratpoison I think it don't fully support Xinerama right know, I'll ask on it's mailing list ;-)