I used to fix the resolution of my screens (Which occur quite often, we have 5 computers having this problem at office and one at home) by setting and adding mode with xrandr in the gdm start script.
This tip was given here https://wiki.ubuntu.com/X/Config/Resolution
But this time in 12.10 I am unable to find any file like that /etc/gdm/Init/Default. Does anyone know if there is still one startup script at the launch of LightDM graphic session ?
Tks