The suspend and hibernate features of Linux can be unreliable. To prevent this feature from being used accidentally, the suspend and hibernate buttons can be disabled in Gnome.
CentOS 5/RHEL 5
1) As root, make sure the gconf-editor package is installed:
# yum -y install gconf-editor
2) Run the gconf-editor program:
Applications->System Tools->Configuration Editor
3) Navigate to:
CentOS / RHEL
The next time Shut Down is selected from the menu, these options will no longer be present.