Mine

Section "ServerFlags"	 
    Option "Xinerama" "On"	 
EndSection	 

Section "Module"	 
    Load "dbe" # Double-Buffering Extension	 
    Load "v4l" # Video for Linux	 
    Load "extmod"	 
    Load "type1"	 
    Load "freetype"	 
    Load "glx"	 
    Load "dri"	 
EndSection	 
	 
...	 
Section "Device"	 
    Identifier "device0"	 
    VendorName "ATI"	 
    BoardName "ATI Radeon"	 
    Driver "radeon"	 
    BusID "PCI:1:0:0"	 
    Screen 0	 
EndSection	 
	 
Section "Device"	 
    Identifier "device1"	 
    BoardName "ATI Radeon"	 
    Driver "radeon"	 
    BusID "PCI:1:0:0"
    Screen 1
EndSection

Section "Monitor"
    Identifier "monitor0"
    Option "DPMS"
EndSection

Section "Monitor"
    Identifier "monitor1"
    Option "DPMS"
EndSection

Section "Screen"
    Identifier "Screen0"
    Device "device0"
    Monitor "monitor0"
    DefaultColorDepth 24
    Subsection "Display"
        Depth 24
        Virtual 1280 1024
        Modes    "1280x1024"
    EndSubsection
EndSection

Section "Screen"
    Identifier "Screen1"
    Device "device1"
    Monitor "monitor1"
    DefaultColorDepth 24
    Subsection "Display"
        Depth 24
        Virtual 1280 1024
        Modes    "1280x1024"
    EndSubsection
EndSection

Section "ServerLayout"
    Identifier "Multihead layout"
    InputDevice "Keyboard1" "CoreKeyboard"
    InputDevice "Mouse0" "CorePointer"
    Screen  "Screen0" 0 0
    Screen  "Screen1" RightOf "Screen0"
EndSection