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 “1280×1024″ “1024×768″ “800×600″ “640×480″
Virtual 2560 1024
EndSubSection
EndSection
Modify it to fits your needs. Cheers to my collegues that tried to help me too 
