After manually modifying the AMDPCSDB, you will want to save it when X isn't running or hard restart the computer following that. When the system is turned off, rebooted, or other graphics changes are made, the manual AMDPCSDB modifications will be wiped out. For our purposes, we had used two ATI Radeon HD 4850 graphics cards. With AMDPCSDB hacking not being sanctioned by AMD, if you run into problems stop by the Phoronix Forums for assistance.
In order to configure the multiple displays, the Linux Catalyst Control Center must be run as root. When MultiView is enabled, most of the layout changes can be applied in real-time without restarting the X.Org server. Within the Display Manager section of this Qt-powered control panel are all of the multiple display settings. In the properties area is the desktop area (resolution) and refresh rate options while in the Multi-Display tab and above that are all of the MultiView features. The desktop configuration can be adjusted through the Multi-Display tab as to whether the selected screen is oriented in relation to the other display powered by the same graphics processor. Cloning a display can also be controlled from this tab. The displays connected to the same graphics card are spanned together using the Big Desktop mode.
Above the tabs each display can be dragged around to change its orientation relative to the other displays. Displays can also be disabled by dragging them outside of the main viewing area. This area is quite slick and makes it extremely easy and straight forward to setup multiple monitors! As you can see from the various screenshots, there are a number of different ways to configure the layout.