From MEPIS Documentation Wiki
If you install the proprietary fglrx driver for your Ati card, you will also have the Ati Catalyst Control Centre (amdcccle from konsole) as well as aticonfig with which you can use to configure your card to an advanced level.
The most probable usage of this command will be:
see http://wiki.cchtml.com/index.php/Configuring for more detail, or:
for detailed info on available parameters.
It is a good idea to only use aticonfig --initial to create a fresh Xorg.conf, and not to modify an existing one. Always back up your original xorg.conf before making any changes.