One of the few things that Linux hasn't done well is allowing the user to add or change monitors.

It looks like this is changing with the new utility xrandr.
I haven't fine tuned this yet (or even tested it much) but I do have a dual head display - with the virtual screen spanning two displays.
I'll come back and document this properly - but for now here's what I did.
First I created this xorg.conf file.
Section "ServerLayout"
Identifier "dual head configuration"
Screen 0 "Screen0" 0 0
InputDevice "Keyboard0" "CoreKeyboard"
EndSection
Section "InputDevice"
Identifier "Keyboard0"
Driver "kbd"
Option "XkbModel" "pc105"
Option "XkbLayout" "gb"
EndSection
Section "Device"
Identifier "Videocard0"
Driver "intel"
Option "monitor-VGA" "vga"
Option "monitor-LVDS" "lvds"
EndSection
Section "Monitor"
Identifier "lvds"
Option "Position" "2560 0"
EndSection
Section "Monitor"
Identifier "vga"
Option "RightOf" "lvds"
EndSection
Section "Screen"
Identifier "Screen0"
Device "Videocard0"
DefaultDepth 16
SubSection "Display"
Viewport 0 0
Depth 16
Modes "2560x1600"
Virtual 5120 1600
EndSubSection
EndSectionThen I restarted my X-windows session and at the console (as a normal user) I ran:
xrandr --output LVDS --mode 1440x900
xrandr --output LVDS --left-of VGAAnd now it works :-)
Links:
[1] http://udrepper.livejournal.com/20187.html
[2] http://www.intellinuxgraphics.org/dualhead.html
[3] http://wiki.debian.org/XStrikeForce/HowToRandR12