Terrible.
Well, first of all you should configure the monitor on its own - forget the dual monitor stuff for the time being.
In Xvidtune, for a resolution of 1680x1050 for the LCD screen of my notebook I have:
HSyncStart 1728 VSyncStart 1052
HSyncEnd 1760 VSyncEnd 1058
HTotal 1840 VTotal 1100
Those settings give as a result:
Resolution 1680x1050
Pixel Clock 119 Mhz
Horizontal Sync 64.67
Vertical Sync 58.79
Try with these settings as a base and once they're set click on "Test" and see what happens.
If that works, start up nvidia-settings and do the setup for dual-monitor. This will generate a xorg.conf containing two "monitor"-sections. Now let xvidtune generate the modeline, modify your xorg.conf with that (one of the two "Monitor"-sections you're supposed to have - one for the laptop monitor, the other one for the external monitor), restart X and see if that works.
You'll have to select in nvidia-settings the option not to have a cloned display. I personally don't use xinerama because the two displays I have have different resolutions and with xinerama it was looking really weird - I use two separate X-desktops (but of course the keyboard and mouse are shared between them).
One big problem of xinerama is that the apps that are not xinerama-aware pop up their graphical stuff in the middle of the virtual display, which is of course between the two monitors, so I always ended up getting message boxes split up between the two screens. With separate screens this problem doesn't occur.
Here is my configuration that generates two separate desktops on the two screens - might be handy as an example (as you can see I don't have a modeline in the monitor sections - only the frequency ranges):
Code:
# nvidia-settings: X configuration file generated by nvidia-settings
# nvidia-settings: version 1.0 (root@quad) Sun Jul 6 18:48:22 CEST 2008
#Section "Extensions"
# Option "Composite" "enable"
#EndSection
Section "ServerLayout"
Identifier "X.org Configured"
Screen 0 "Screen0" 0 0
Screen 1 "Screen1" 1440 0
InputDevice "Mouse0" "CorePointer"
InputDevice "Keyboard0" "CoreKeyboard"
EndSection
Section "Files"
FontPath "/usr/share/fonts/misc/"
FontPath "/usr/share/fonts/TTF/"
FontPath "/usr/share/fonts/Type1/"
FontPath "/usr/share/fonts/CID/"
FontPath "/usr/share/fonts/75dpi/"
FontPath "/usr/share/fonts/100dpi/"
EndSection
Section "Module"
Load "dbe"
# Load "dri"
Load "extmod"
Load "glx"
Load "record"
Load "xtrap"
Load "freetype"
Load "type1"
EndSection
Section "ServerFlags"
# Removed Option "Xinerama" "1"
Option "BlankTime" "20"
Option "Xinerama" "0"
EndSection
Section "InputDevice"
Identifier "Keyboard0"
Driver "kbd"
Option "XkbLayout" "ch"
Option "XkbVariant" "de"
EndSection
Section "InputDevice"
## Option "ChordMiddle"
## Option "Buttons" "2"
## Option "ZAxisMapping" "4 5 6 7"
# Option "MinSpeed" "1.00"
# Option "MaxSpeed" "2.40"
# Option "AccelFactor" "0.090"
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "auto"
Option "Device" "/dev/input/mouse0" #Touchpad
EndSection
Section "Monitor"
Identifier "Monitor0"
VendorName "Unknown"
ModelName "Samsung SyncMaster"
HorizSync 30.0 - 81.0
VertRefresh 56.0 - 75.0
EndSection
Section "Monitor"
Identifier "Monitor1"
VendorName "Unknown"
ModelName "CRT-1"
HorizSync 28.0 - 80.0
VertRefresh 43.0 - 75.0
EndSection
Section "Device"
Identifier "Card0"
Driver "nvidia"
VendorName "nVidia Corporation"
BoardName "Unknown Board"
Option "Coolbits" "1"
BusID "PCI:1:0:0"
EndSection
Section "Device"
Identifier "Videocard0"
Driver "nvidia"
VendorName "NVIDIA Corporation"
BoardName "GeForce 8800 GTS 512"
BusID "PCI:1:0:0"
Screen 0
EndSection
Section "Device"
Identifier "Videocard1"
Driver "nvidia"
VendorName "NVIDIA Corporation"
BoardName "GeForce 8800 GTS 512"
BusID "PCI:1:0:0"
Screen 1
EndSection
Section "Screen"
Identifier "Screen0"
Device "Videocard0"
Monitor "Monitor0"
DefaultDepth 24
Option "TwinView" "0"
Option "metamodes" "DFP: 1440x900 +0+0"
SubSection "Display"
Depth 24
EndSubSection
EndSection
Section "Screen"
Identifier "Screen1"
Device "Videocard1"
Monitor "Monitor1"
DefaultDepth 24
Option "TwinView" "0"
Option "metamodes" "CRT: 1280x1024 +0+0"
EndSection
p.s.: ah, damn, you don't have an nVidia GPU, right? Well, in this case just play around with xvidtune and my config example.