HP with docking station and external monitor

I'm trying to create an Xorg config which let's me run 1680x1050 on my internal display on my laptop and 1280x1024 when I connect an external display via the VGA port or if I dock the laptop in a docking station. I have a HP nc8430 laptop with an ATI graphics card. I run Feisty with the proprietary fglrx driver.

I managed to get different resolutions on my displays when I defined an additional device/screen/monitor. However, then my laptop is always the primary. If I start my computer docked with the lid closed my external display get's the 1680x1050 resolution which it is unable to handle.

I read some other answers and I found a configuration which I use right now. The problem with this config is that even though both displays use their respective correct resolution the desktop is too big on the external displays which requires me to scroll.

So; question is: How do I rewrite my xorg.conf to always run 1680x1050 on my internal display and 1280x1024 on my external display and always having the active one as my primary?

Current xorg.conf:

# /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 "ServerLayout"
 Identifier "Default Layout"
 Screen "Internal"
 #Screen "External" RightOf "Internal"
 InputDevice "Generic Keyboard"
 InputDevice "Configured Mouse"
 InputDevice "stylus" "SendCoreEvents"
 InputDevice "cursor" "SendCoreEvents"
 InputDevice "eraser" "SendCoreEvents"
 InputDevice "Synaptics Touchpad"
EndSection

Section "Files"

 # path to defoma fonts
 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"
 FontPath "/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
EndSection

Section "Module"
 Load "i2c"
 Load "bitmap"
 Load "ddc"
 Load "dri"
 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" "se"
 Option "XkbOptions" "lv3:ralt_switch"
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 "HorizScrollDelta" "0"
EndSection

Section "InputDevice"

       # /dev/input/event
       # for USB
 Identifier "stylus"
 Driver "wacom"
 Option "Device" "/dev/wacom" # Change to
 Option "Type" "stylus"
 Option "ForceDevice" "ISDV4" # Tablet PC ONLY
EndSection

Section "InputDevice"

       # /dev/input/event
       # for USB
 Identifier "eraser"
 Driver "wacom"
 Option "Device" "/dev/wacom" # Change to
 Option "Type" "eraser"
 Option "ForceDevice" "ISDV4" # Tablet PC ONLY
EndSection

Section "InputDevice"

       # /dev/input/event
       # for USB
 Identifier "cursor"
 Driver "wacom"
 Option "Device" "/dev/wacom" # Change to
 Option "Type" "cursor"
 Option "ForceDevice" "ISDV4" # Tablet PC ONLY
EndSection

Section "Monitor"
 Identifier "Internal Display"
 HorizSync 28.0 - 84.0
 VertRefresh 43.0 - 60.0
 Option "DPMS"
EndSection

#Section "Monitor"
# Identifier "External Display"
# Option "VendorName" "ATI Proprietary Driver"
# Option "ModelName" "Generic Autodetecting Monitor"
# Option "DPMS" "true"
#EndSection

Section "Device"
 #Option "OpenGLOverlay" "off"
 Identifier "Generic Video Card"
 Driver "fglrx"
 Option "EnableMonitor" "crt1,lvds"
 Option "VideoOverlay" "on"
 BusID "PCI:1:0:0"
 Screen 0
EndSection

#Section "Device"
# Identifier "VGA"
# Driver "fglrx"
# BusID "PCI:1:0:0"
# Screen 1
#EndSection

Section "Screen"
 Identifier "Internal"
 Device "Generic Video Card"
 Monitor "Internal Display"
 DefaultDepth 24
 Option "MetaModes" "1680x1050,1280x1024"
 SubSection "Display"
 Virtual 1280 1024
  Depth 24
  Modes "1680x1050" "1280x1024"
 EndSubSection
EndSection

#Section "Screen"
# Identifier "External"
# Device "VGA"
# Monitor "External Display"
# DefaultDepth 24
# SubSection "Display"
# Depth 24
# Modes "1280x1024"
# EndSubSection
#EndSection

Section "DRI"
 Mode 0666
EndSection

Section "Extensions"
 Option "Composite" "0"
EndSection