I’ve just solved a problem with dual head at work and I want to share this.
The “man” that gave me a hand was here and thaks to him, this is my working xorg.conf configuration:
Section "Device"
Identifier "ATI Technologies Inc RV280 [Radeon 9200 PRO]"
Driver "ati"
BusID "PCI:3:2:0"
Option "monitor-DVI-0" "Dell E176FP"
Option "monitor-VGA-0" "Dell E196FP"
EndSection
Section "Monitor"
Identifier "Dell E196FP"
Option "DPMS"
HorizSync 31-83
VertRefresh 56-76
EndSection
Section "Monitor"
Identifier "Dell E176FP"
Option "DPMS"
HorizSync 31-80
VertRefresh 56-75
Option "RightOf" "Dell E196FP"
EndSection
Section "Screen"
Identifier "Default Screen"
Device "ATI Technologies Inc RV280 [Radeon 9200 PRO]"
Monitor "Dell E196FP"
DefaultDepth 16
SubSection "Display"
Modes "1280x1024" "1024x768" "800x600" "640x480"
Virtual 2560 1024
EndSubSection
EndSection
Modify it to fits your needs. Cheers to my collegues that tried to help me too 
Worked for me too ! One screen only, and worked OK on standard generated Xorg.conf . But, changing Driver into “radeon” left me without X ;( Learned here that I needed “ati”. Thanks, greets from Netherlands
Comment by eerstkoffie — February 25, 2010 @ 12:30 pm