J'ai une radeon 9700... je te donne mon xorg pour que tu puisses comparer
# Xorg configuration created by system-config-display
Section "ServerLayout"
Identifier "single head configuration"
Screen 0 "Screen0" 0 0
InputDevice "Keyboard0" "CoreKeyboard"
InputDevice "Synaptics" "CorePointer"
EndSection
Section "InputDevice"
Identifier "Keyboard0"
Driver "kbd"
Option "XkbModel" "pc105"
Option "XkbLayout" "fr"
Option "XkbVariant" "latin9"
EndSection
Section "InputDevice"
Identifier "Synaptics"
Driver "synaptics"
Option "Device" "/dev/input/mice"
Option "Protocol" "auto-dev"
Option "Emulate3Buttons" "yes"
EndSection
Section "Monitor"
Identifier "Monitor0"
ModelName "LCD Panel 1280x800"
HorizSync 31.5 - 90.0
VertRefresh 59.9 - 60.1
Option "dpms"
EndSection
Section "Device"
Identifier "Videocard0"
Driver "radeon"
EndSection
Section "Screen"
Identifier "Screen0"
Device "Videocard0"
Monitor "Monitor0"
DefaultDepth 24
SubSection "Display"
Viewport 0 0
Depth 24
Modes "1280x800" "1280x720" "1152x864" "1024x768" "800x600" "640x480"
EndSubSection
EndSection