I finally got dual screen working on my Inspiron 8100. It took me
about two hours: I had a working configuration but I needed a hard
reboot! I have used Xorg 7.2 on Ubuntu 7.04. Here is the relevant
snippet of my xorg.conf:
Section "Device"
Identifier "Radeon"
Driver "radeon"
Option "MergedFB" "true"
Option "CRT2Hsync" "30-81"
Option "CRT2VRefresh" "56-75"
Option "MonitorLayout" "LVDS, CRT"
Option "CRT2Position" "LeftOf"
Option "MergedNonRectangular" "true"
Option "MetaModes" "1600x1200-1280x1024"
EndSection
Section "Screen"
Identifier "Main Screen"
Device "Radeon"
Monitor "Generic Monitor"
DefaultDepth 24
SubSection "Display"
Depth 24
Modes "1600x1200" "1280x1024"
Virtual 2880 1200
EndSubSection
EndSection