I've recently installed Fedora 18 as a server in text mode only ; After a few days I wanted the gnome desktop ;
only two commands for that :
yum groupinstall gnome-desktop
startx &
Not having a powerful videocard in this server , I've switched to gnome fallback mode aka gnome-2-like graphical mode :
System Settings > System Info -> Fallback Mode
http://www.dedoimedo.com/computers/gnome-3-fallback.html