Where is the X.org config file? How do I configure X there?

As Ubuntu 10.10 seems to neither detect my graphics card (Intel 82852/855GM) automatically nor use the corresponding Intel driver even after manually installing it, I am looking into manually configuring X (shouldn't I?). Where can I find the configuration files I need to edit?

The xorg.conf does not exist by default any more. You CAN create one though.

Boot into recovery mode and select Root Shell. Then run:

X -configure

Then:

cp /root/xorg.conf.new /etc/X11/xorg.conf

Reboot and you can edit the new Xorg.conf.

The configurations files are at /usr/share/X11/xorg.conf.d

They are:

10-evdev.conf

11-evdev-quirks.conf

50-vmmouse.conf

50-wacom.conf

51-synaptics-quirks.conf

Check the current manual.

If you create a xorg.conf file the configurations of this file will prevail.
Also check this answer.