once you run
yum groupinstall " KDE (K Desktop Environment)"
there will on the GDM ( gnome) login window an option to select gnome or kde
after you type in your password BUT BEFORE YOU HIT ENTER
boot into ked and make sure it runs
then add the desktop file and reboot
now using kde to start gnome you will need to set ( in kde ) the screensaver settings, the 10 min time out before the screen locks . Also the login theme must be set in kde .
the ked settings for the screen lock WILL BE USED for Gnome