The key combination Ctrl+Alt+Backspace to kill the X server has been disabled by default as a decision of the upstream Xorg project. You can change the default by adding the following section to your xorg.conf file. If one does not exist, you can create it manually at /etc/X11/xorg.conf using a text editor and Xorg will honor that setting.

Section "ServerFlags"
Option "DontZap" "false"
EndSection

If you use kickstart or want to use scripts to change this setting automatically across multiple systems, you can use the following snippet:

%post

grep -q -s DontZap /etc/X11/xorg.conf
append=$?
if [ $append -ne 0 ]; then
  cat >> /etc/X11/xorg.conf << EOF
  Section "ServerFlags"
  Option "DontZap" "false"
  EndSection
  EOF
fi

%end

The Xorg project has changed the default DontZap setting to "true" after complaints from desktop users that accidentally hit Ctrl+Alt+Backspace when trying to type Alt+Backspace, Ctrl+Backspace, or Shift+Backspace, or who had StickyKeys enabled. Ctrl+Alt+Backspace is also a keyboard shortcut for deleting certain expressions in C and Java modes in Emacs.

Refer to the Xorg third-party drivers page for detailed guidelines on using third-party video drivers: http://fedoraproject.org/wiki/Xorg/3rdPartyVideoDrivers