Try this one I knocked together
/etc/X11/xorg.conf
Code:
Section "Monitor"
Identifier "Monitor0"
HorizSync 30-40
VertRefresh 47-90
EndSection
Section "Device"
Identifier "Card0"
Driver "vesa"
EndSection
Section "Screen"
Identifier "Screen0"
Monitor "Monitor0"
Device "Card0"
DefaultDepth 16
SubSection "Display"
Depth 16
Modes "640x480_60"
EndSubSection
EndSection
Do you know what the graphics adapter is? There may be something more suitable than the vesa driver, but it's a starting point anyway.
//edit: I see you say it's some kind of ATI graphics, you could try the "ati" driver which is wrapper which should select the best driver automatically, but see if it works and gives the correct resolution and refresh rate with the vesa driver first.