Many modern day linux distributions are no more using a xorg.conf file to handle graphics and screen resolution issues. Instead the HAL (Hardware Abstraction Layer) is being used to do all these. Still if you want to get back the xorg.conf style of tweaking your display, you simply need to install system-config-display on a RedHat based system.
To install use the following command:
sudo yum -y install system-config-display
After the install, you may now see that there is a xorg.conf file in the /etc/X11/ directory, with pre-filled entries. Should you need to reconfigure your Xorg system then you can use the following command to do so:
sudo X -reconfigure