dual monitor problem

[Nicolas Mommaerts]

I have a dual monitor setup, which works fine in Gnome. I'm NOT using
Xinerama and don't want to either. When I start xfce4 only my main
monitor is used. I can move the mouse to my other monitor though, but
that screen is just black and the mouse cursor changes to a cross (the
default arrow in X?) I searched the maillists and encountered  two
people with the same problem but no solution...