Ik heb mijn twee beeldschermen met succes aan de praat, het xorg.conf manueel aanpassen:
$ gedit /etc/X11/xorg.conf
De mijne ziet er als volgt uit:
# /etc/X11/xorg.conf (xorg X Window System server configuration file)
#
# This file was generated by dexconf, the Debian X Configuration tool, using
# values from the debconf database.
#
# Edit this file with caution, and see the xorg.conf(5) manual page.
# (Type "man xorg.conf" at the shell prompt.)
#
# This file is automatically updated on xserver-xorg package upgrades *only*
# if it has not been modified since the last upgrade of the xserver-xorg
# package.
#
# If you have edited this file but would like it to be automatically updated
# again, run the following command:
# sudo dpkg-reconfigure -phigh xserver-xorg
Section "Files"
Fontpath "/usr/share/fonts/X11/misc"
Fontpath "/usr/share/fonts/X11/cyrillic"
Fontpath "/usr/share/fonts/X11/100dpi/:unscaled"
Fontpath "/usr/share/fonts/X11/75dpi/:unscaled"
Fontpath "/usr/share/fonts/X11/Type1"
Fontpath "/usr/share/fonts/X11/100dpi"
Fontpath "/usr/share/fonts/X11/75dpi"
# path to defoma fonts
Fontpath "/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
EndSection
Section "Module"
Load "i2c"
Load "bitmap"
Load "ddc"
Load "extmod"
Load "freetype"
Load "glx"
Load "int10"
Load "vbe"
EndSection
Section "InputDevice"
Identifier "Generic Keyboard"
Driver "kbd"
Option "CoreKeyboard"
Option "XkbRules" "xorg"
Option "XkbModel" "pc105"
Option "XkbLayout" "us"
Option "XkbVariant" "alt-intl"
EndSection
Section "InputDevice"
Identifier "Configured Mouse"
Driver "mouse"
Option "CorePointer"
Option "Device" "/dev/input/mice"
Option "Protocol" "ImPS/2"
Option "ZAxisMapping" "4 5"
Option "Emulate3Buttons" "true"
EndSection
Section "InputDevice"
Driver "wacom"
Identifier "stylus"
Option "Device" "/dev/input/wacom"
Option "Type" "stylus"
Option "ForceDevice" "ISDV4"# Tablet PC ONLY
EndSection
Section "InputDevice"
Driver "wacom"
Identifier "eraser"
Option "Device" "/dev/input/wacom"
Option "Type" "eraser"
Option "ForceDevice" "ISDV4"# Tablet PC ONLY
EndSection
Section "InputDevice"
Driver "wacom"
Identifier "cursor"
Option "Device" "/dev/input/wacom"
Option "Type" "cursor"
Option "ForceDevice" "ISDV4"# Tablet PC ONLY
EndSection
Section "Device"
Identifier "nVidia Corporation G70 [GeForce 7300 GT]"
Driver "nvidia"
Busid "PCI:2:0:0"
Option "AddARGBVisuals" "True"
Option "AddARGBGLXVisuals" "True"
Option "NoLogo" "True"
EndSection
Section "Monitor"
Identifier "M-SERIAL"
Option "DPMS"
Horizsync 28-64
Vertrefresh 43-60
EndSection
Section "Screen"
Identifier "Default Screen"
Device "nVidia Corporation G70 [GeForce 7300 GT]"
Monitor "M-SERIAL"
Defaultdepth 24
Option "TwinView" "true"
Option "SecondMonitorHorizSync" "30-70"
Option "SecondMonitorVertRefresh" "50-120"
Option "MetaModes" "1280x1024, 1280x1024; 1280x1024, 1280x1024;"
Option "TwinViewOrientation" "RightOf"
SubSection "Display"
Depth 1
Modes "1280x1024" "1024x768" "832x624" "800x600" "720x400" "640x480"
EndSubSection
SubSection "Display"
Depth 4
Modes "1280x1024" "1024x768" "832x624" "800x600" "720x400" "640x480"
EndSubSection
SubSection "Display"
Depth 8
Modes "1280x1024" "1024x768" "832x624" "800x600" "720x400" "640x480"
EndSubSection
SubSection "Display"
Depth 15
Modes "1280x1024" "1024x768" "832x624" "800x600" "720x400" "640x480"
EndSubSection
SubSection "Display"
Depth 16
Modes "1280x1024" "1024x768" "832x624" "800x600" "720x400" "640x480"
EndSubSection
SubSection "Display"
Depth 24
Modes "1280x1024" "1024x768" "832x624" "800x600" "720x400" "640x480"
EndSubSection
EndSection
Section "ServerLayout"
Identifier "Default Layout"
screen "Default Screen"
Inputdevice "Generic Keyboard"
Inputdevice "Configured Mouse"
Inputdevice "stylus" "SendCoreEvents"
Inputdevice "cursor" "SendCoreEvents"
Inputdevice "eraser" "SendCoreEvents"
EndSection
Section "DRI"
Mode 0666
EndSection
Je moet in ieder geval nog een section "Monitor" aanmaken, bij mij zijn het twee dezelfde. Dan moet je bij section "Screen" het volgende erin passen:
Option "TwinView" "true"
Option "SecondMonitorHorizSync" "30-70"
Option "SecondMonitorVertRefresh" "50-120"
Option "TwinViewOrientation" "RightOf"
die getallen achter SeconMonitorHorizSync moet je aanpassen aan je eigen wensen. Het beschrijft de plaats waarop je tweede monitor moet komen. Het hangt dus af van de resolutie van je standaarbeeldscherm. Althans, dat was het geloof ik

.
Dit staat iig bij mijn eerste beeldscherm..
Section "Monitor"
Identifier "M-SERIAL"
Option "DPMS"
Horizsync 28-64
Vertrefresh 43-60
edit:
in de manual ($ man zorg.conf) het volgende over de Sync:
HorizSync horizsync-range
gives the range(s) of horizontal sync frequencies supported by
the monitor. horizsync-range may be a comma separated list of
either discrete values or ranges of values. A range of values
is two values separated by a dash. By default the values are in
units of kHz. They may be specified in MHz or Hz if MHz or Hz
is added to the end of the line. The data given here is used by
the Xorg server to determine if video modes are within the spec