Code:
Section "Screen"
Identifier "Screen 1"
Device "nVidia GeForce"
Monitor "Samsung SyncMaster 710N"
DefaultDepth 24
Subsection "Display"
Depth 8
Modes "1280x1024" "1024x768" "800x600" "640x480"
ViewPort 0 0
EndSubsection
Subsection "Display"
Depth 16
Modes "1280x1024" "1024x768" "800x600" "640x480"
ViewPort 0 0
EndSubsection
Subsection "Display"
Depth 24
Modes "1280x1024" "1024x768" "800x600" "640x480"
ViewPort 0 0
EndSubsection
EndSection
add modes to you xorg.conf..... change values, if you need to