I was pleasantly surprised to see that the fight to get dual screens working properly with the ATI graphics card wasn’t as difficult as it has been in the past. The restricted hardware manager didn’t lock up on me after activating the ATI driver, but I still couldn’t get big desktop to work.
When trying to set up big desktop through aticonfig in the terminal I got Error: Options, e.g. --dtop and --desktop-setup, are not supported when RandR 1.2 is enabled. I had no idea what that meant but I did a quick google search and found that someone had reported a bug with the same problem. Another person posted something that fixed it for me.
Login to a tty (ctrl+alt F1) and type sudo killall gdm. Type sudo nano (or gedit, whichever you prefer) /etc/ati/amdpcsdb to edit the file. a) Go to the [AMDPCSROOT/SYSTEM/DDX] section and add EnableRandR12=Sfalse. Type this into a terminal, sudo nano (or gedit) /etc/X11/xorg.conf, to open the xorg.conf file. Under the “Device” section add these options on separate lines: Option "EnableRandR12" "false" and Option "DesktopSetup" "horizontal". Now just restart your computer and it should be good to go.xorg.conf file:
Section “ServerLayout”
Identifier “aticonfig Layout”
Screen 0 “Default Screen” 0 0
EndSection
Section “Files”
EndSection
Section “Module”
Load “glx”
EndSection
Section “Monitor”
Identifier “Configured Monitor”
EndSection
Section “Device”
Identifier “Configured Video Device”
Driver “fglrx”
Option “EnableRandR12″ “false”
Option “DesktopSetup” “horizontal”
BusID “PCI:1:0:0″
EndSection
Section “Screen”
Identifier “Default Screen”
Device “Configured Video Device”
Monitor “Configured Monitor”
DefaultDepth 24
EndSection
