Dual monitor setup: xrandr versus xorg.conf

You forgot a "Monitor" entry in the Screen section.

See below:

Section "Device"
        Identifier     "nvidia"
        Driver "nouveau"
        Option "Monitor-DVI-D-0" "samsung"
        Option "Monitor-VGA-1" "acer"
EndSection


Section "Monitor"
          Identifier   "samsung"
        Option "PreferredMode" "1280x1024_60.00"
EndSection


Section "Monitor"
          Identifier   "acer"
        Option "PreferredMode" "1280x1024_60.00"
          Option "RightOf" "samsung"
EndSection

Section "Screen"
    Identifier "screen1"
   Monitor "samsung"
    DefaultDepth 24
      SubSection "Display"
       Depth      24
       Virtual 2560 2048
      EndSubSection
    Device "nvidia"
EndSection

Section "ServerLayout"
    Identifier "layout1"
    Screen "screen1"
EndSection

I have Fedora 14 with dual monitors specified in xorg.conf, using the ATI proprietary fglrx driver, with the desktop spread across both monitors.

I believe I used aticonfig --initial=dual-head to generate my xorg.conf a year or so ago and tweaked it a bit. Try that. For reference, here is my xorg.conf.

Section "ServerLayout"
    Identifier     "aticonfig Layout"
    Screen      0  "aticonfig-Screen[0]-0" 0 0
EndSection

Section "Files"
EndSection

Section "Module"
EndSection

Section "Monitor"
    Identifier   "aticonfig-Monitor[0]-0"
    Option      "VendorName" "ATI Proprietary Driver"
    Option      "ModelName" "Generic Autodetecting Monitor"
    Option      "DPMS" "true"
EndSection

Section "Monitor"
    Identifier   "0-DFP3"
    Option      "VendorName" "ATI Proprietary Driver"
    Option      "ModelName" "Generic Autodetecting Monitor"
    Option      "DPMS" "true"
    Option      "PreferredMode" "1920x1200"
    Option      "TargetRefresh" "60"
    Option      "Position" "0 0"
    Option      "Rotate" "normal"
    Option      "Disable" "false"
EndSection

Section "Monitor"
    Identifier   "0-DFP4"
    Option      "VendorName" "ATI Proprietary Driver"
    Option      "ModelName" "Generic Autodetecting Monitor"
    Option      "DPMS" "true"
    Option      "PreferredMode" "1280x1024"
    Option      "TargetRefresh" "60"
    Option      "Position" "1920 176"
    Option      "Rotate" "normal"
    Option      "Disable" "false"
EndSection

Section "Device"
    Identifier  "aticonfig-Device[0]-0"
    Driver      "fglrx"
    Option      "Monitor-DFP3" "0-DFP3"
    Option      "Monitor-DFP4" "0-DFP4"
    BusID       "PCI:2:0:0"
EndSection

Section "Screen"
    Identifier "aticonfig-Screen[0]-0"
    Device     "aticonfig-Device[0]-0"
    Monitor    "aticonfig-Monitor[0]-0"
    DefaultDepth     24
    SubSection "Display"
        Viewport   0 0
        Virtual   3200 3200
        Depth     24
    EndSubSection
EndSection