That's not what was meant by the comment.
You need to create a file named /etc/X11/xorg.conf and edit it to suit your hardware and what you require.
I believe you are using tc-4.x - if I remember correctly, this means you will need to create a full xorg..conf rather than just a "snippet" containing details of what you want to change.
Essentially, your xorg.conf needs to contain something like this (as well as the other standard sections): Section "Screen"
Identifier "Default Screen"
Device "Intel GM45"
Monitor "Whatever"
DefaultDepth 16
SubSection "Display"
Depth 16
Modes "800x600_75.00"
EndSubSection
EndSection
You will no doubt need to proceed on a trial and error basis - modify xorg.conf, exit to the prompt, startx, check Xorg.0.log and repeat...