C'est ça. Voir dans la section Screen :
Section "Screen"
Identifier "Screen 1"
Device "ATI Xpert@Work"
Monitor "My Monitor"
DefaultDepth 24
Subsection "Display"
Depth 8
Modes "640x480" "800x600" "1024x768" "1280x1024"
ViewPort 0 0
EndSubsection
Subsection "Display"
Depth 16
Modes "1280x1024" "1024x768" "800x600" "640x480"
ViewPort 0 0
EndSubsection
Subsection "Display"
Depth 24
Modes "1600x1200" "1280x1024" "1024x768" "640x480"
ViewPort 0 0
EndSubsection
EndSection
En italique, les lignes les plus importantes, celles qu'il y aura à changer ou à rajouter.