I got xinerama to work with my Radeon 8500, here's my config file. It works pretty well although I just changed some setting I can't remember and it locks up my computer. Oh well. I'll fix it eventually. This should work (just change the PCI Bus and monitor refresh rates.
Section "Files"
FontPath "unix/:7100"
FontPath "/usr/lib/X11/fonts/misc"
FontPath "/usr/lib/X11/fonts/cyrillic"
FontPath "/usr/lib/X11/fonts/100dpi/:unscaled"
FontPath "/usr/lib/X11/fonts/75dpi/:unscaled"
FontPath "/usr/lib/X11/fonts/Type1"
FontPath "/usr/lib/X11/fonts/Speedo"
FontPath "/usr/lib/X11/fonts/100dpi"
FontPath "/usr/lib/X11/fonts/75dpi"
EndSection
Section "Module"
# Load "GLcore"
Load "bitmap"
Load "dbe"
Load "ddc"
# Load "dri"
Load "extmod"
Load "freetype"
# Load "glx"
Load "int10"
# Load "pex5"
Load "record"
Load "speedo"
Load "type1"
# Load "vbe"
# Load "xie"
EndSection
Section "InputDevice"
Identifier "Generic Keyboard"
Driver "keyboard"
Option "CoreKeyboard"
Option "XkbRules" "xfree86"
Option "XkbModel" "pc104"
Option "XkbLayout" "us"
EndSection
Section "InputDevice"
Identifier "Configured Mouse"
Driver "mouse"
Option "CorePointer"
Option "Device" "/dev/psaux"
Option "Protocol" "ImPS/2"
Option "Emulate3Buttons" "true"
Option "ZAxisMapping" "4 5"
Option "Resolution" "500"
EndSection
Section "Device"
Identifier "Ati1"
Driver "radeon"
Option "crt_screen"
BusID "PCI:2:0:0"
Screen 1
EndSection
Section "Device"
Identifier "Ati2"
Driver "radeon"
Option "crt_screen"
BusID "PCI:2:0:0"
EndSection
Section "Monitor"
Identifier "A90f"
HorizSync 30-100
VertRefresh 50-160
Option "DPMS"
EndSection
Section "Monitor"
Identifier "G790"
HorizSync 30-86
# VertRefresh 50-150
VertRefresh 60
Option "DPMS"
EndSection
Section "Screen"
Identifier "Screen1"
Device "Ati1"
Monitor "A90f"
DefaultDepth 24
DefaultFbBPP 32
SubSection "Display"
Depth 24
Modes "1600x1200"
EndSubSection
EndSection
Section "Screen"
Identifier "Screen2"
Device "Ati2"
Monitor "G790"
DefaultDepth 24
DefaultFbBPP 32
SubSection "Display"
Depth 24
Modes "1600x1200"
EndSubSection
EndSection
Section "ServerLayout"
Identifier "Desktop"
# Screen "Screen2" RightOf "Screen1"
Screen "Screen1" 0 0
Screen "Screen2" LeftOf "Screen1"
InputDevice "Generic Keyboard"
InputDevice "Configured Mouse"
Option "Xinerama"
EndSection
Section "DRI"
Mode 0666
EndSection
Marge: Well I think we should spend the money on something the whole town can be proud of.
Homer: Like a giant billboard that says "No Fat Chicks"?
The Simpsons - 9F10 - S04E12
Marge vs. the Monorail