This is my current xorg.conf for a dual head setup with a Nvidia GPU on Arch Linux.

Section "ServerLayout"
    Identifier      "Layout0"
    Screen          0  "Screen0" 0 0
    InputDevice     "Keyboard0" "CoreKeyboard"
    InputDevice     "Mouse0" "CorePointer"
EndSection

Section "Files"
EndSection

Section "Module"
    Load            "dbe"
    Load            "extmod"
    Load            "type1"
    Load            "freetype"
    Load            "glx"
EndSection

Section "ServerFlags"
    Option          "Xinerama" "0"
    Option          "AutoAddDevices" "False"
EndSection

Section "InputDevice"
    Identifier      "Mouse0"
    Driver          "mouse"
    Option          "CorePointer"
    Option          "Device"        "/dev/input/mice"
    Option          "Protocol"      "ImPS/2"
    Option          "Emulate3Buttons"   "true"
    Option          "ZAxisMapping"      "4 5"
EndSection

Section "InputDevice"
    Identifier      "Keyboard0"
    Driver          "kbd"
    Option          "XkbRules" "xorg"
    Option          "XkbModel" "pc105"
    Option          "XkbLayout" "de"
    Option          "XkbVariant" "nodeadkeys"
EndSection

Section "Monitor"
    Identifier      "Monitor0"
    VendorName      "Unknown"
    ModelName       "STN SAMTRON"
    HorizSync       30.0 - 81.0
    VertRefresh     56.0 - 75.0
    Option          "DPMS"
EndSection

Section "Device"
    Identifier      "Device0"
    Driver          "nvidia"
    VendorName      "NVIDIA Corporation"
    BoardName       "GeForce 6600 GT"
    Option          "RenderAccel"           "True"
    Option          "NoLogo"                "true"
    Option          "DPI"                   "96 x 96"
EndSection

Section "Screen"
    Identifier      "Screen0"
    Device          "Device0"
    Monitor         "Monitor0"
    DefaultDepth    24
    Option          "TwinView" "1"
    Option          "TwinViewXineramaInfoOrder" "CRT-0"
    Option          "metamodes" "CRT: nvidia-auto-select +1280+0, DFP: nvidia-auto-select +0+0"
    SubSection      "Display"
        Depth       24
    EndSubSection
EndSection