It took me 20 minutes so I thought I shared my configuration:

# 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 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"
EndSection

Section "InputDevice"
Identifier "Generic Keyboard"
Driver "kbd"
Option "CoreKeyboard"
Option "XkbRules" "xorg"
Option "XkbModel" "pc104"
Option "XkbLayout" "us"
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"
Identifier "Synaptics Touchpad"
Driver "synaptics"
Option "SendCoreEvents" "true"
Option "Device" "/dev/psaux"
Option "Protocol" "auto-dev"
Option "HorizEdgeScroll" "0"
EndSection

Section "Device"
Identifier "Intel Corporation Mobile 945GM/GMS, 943/940GML Express Integrated Graphics Controller"
Driver "intel"
BusID "PCI:0:2:0"
EndSection

Section "Monitor"
Option "DPMS"
Identifier "Samsung2243LNX"
VendorName "Samsung"
ModelName "SyncMaster 2243LNX"
HorizSync 31.4 - 80.0
VertRefresh 56.000 - 75.000
Modeline "1680x1050" 146.25 1680 1784 1960 2240 1050 1053 1059 1089
EndSection

Section "Screen"
Identifier "Default Screen"
Device "Intel Corporation Mobile 945GM/GMS, 943/940GML Express Integrated Graphics Controller"
Monitor "Samsung2243LNX"
DefaultDepth 24
SubSection "Display"
Depth 24
Modes "1680x1050" "1600x1200" "1440x1440" "1280x1024" "1152x864" "1024x768" "832x624" "800x600" "720x400" "640x480"
Virtual 2960 1050
EndSubSection
EndSection

Section "ServerLayout"
Identifier "Default Layout"
Screen "Default Screen"
InputDevice "Generic Keyboard"
InputDevice "Configured Mouse"

InputDevice "Synaptics Touchpad"
EndSection

For more details, please check out another post I wrote about setting up a Dual screen on Ubuntu Gutsy with Toshiba laptop Intel 945