The Beauty Of X
Running X is fairly painless now, compared to a few years back. If you had to manually edit xorg.conf and get it wrong. Aaaaaargh.
Anyhow, when you install X today, it auto-configures itself.
Sometimes you find you have no xorg.conf file. It normally resides in /etc/X11/xorg.conf.
If your xorg.conf file has disappeared, here's how to generate another.
First you need to kill X. Switch to the console by pressing Ctrl-Alt-F1 or Ctrl-Alt-F2 or Ctrl-Alt-F3.
As root user, stop your display manager, if your using one.
# /etc/init.d/kdm stop
# /etc/init.d/gdm stop
# /etc/init.d/xdm stop
Next change to X11 directory
# cd /etc/X11
# Xorg -configure
Follow the on-screen instructions, which create your new xorg.conf.
On completion, restart X.