an example :
Code:
Section "Monitor"
Identifier "aticonfig-Monitor[0]"
Option "VendorName" "ATI Proprietary Driver"
Option "ModelName" "Generic Autodetecting Monitor"
Option "DPMS" "true"
HorizSync 31.0 - 31.0
VertRefresh 70.0 - 70.0
EndSection
Section "Screen"
Identifier "aticonfig-Screen[0]"
Device "aticonfig-Device[0]"
Monitor "aticonfig-Monitor[0]"
DefaultDepth 24
SubSection "Display"
Viewport 0 0
Depth 24
Modes "1280x1024"
EndSubSection
(mine)
Section "monitor" describes the physical characteristics that you want X to use with the monitor attached; HorizSynch (in KHZ) is used to do something, not sure what. Vert Refresh in Hz is the number of times your screen is repainted per second. Apparently you can do some mathemagical function to these and get your possible screen resolution.
HorizSynch/VertRefresh are only likely to be found through your monitor's back panel, OSD or manual.
Section "Screen" is the combination of everything specified in xorg.config to actually give you a gui;
modes 1280x1024 is the pixel resolution ( obv) and in your case i'm assuming the extras are added on by the proprietary graphic driver to take advantage of it's keen features of niftiness.
if you've got a known good HorizSynch/VertRefresh; its a matter of trial and error to find the right resolution, but most sane displays will run at the usual suspects, or at least 800*600