Running Opensuse 11.0 on a Dell laptop with second display.

When the second display is an Asus widescreen monitor (I don't remember the model number), I can successfully Activate Dual Head Mode, and select Xinerama Multi-head to get one big display out of both screens. This works fine.

But when the second display is a Dell E171FP, it always acts as a clone of the laptop screen, irrespective of the Dual Head display settings. Also, changing the resolution setting for the second display does not change the screen playing area.

[When I use the Dell E171FP as a second display to extend the desktop under Windows XP, it works OK].

Any ideas why the Dell E171FP does not work as a second display under Opensuse 11.0?