This issue raise for those who is logged in directly to GNOME or KDE without having option to Change both from login screen,It can be resolved with a few steps
For the user convinience GNOME and KDE can be selected from the Login area,
the Default Login managers have option to select Sessions on the bottom ( i m dealing Fedora 12), any how if we set a users Password with No password the system will not prompt for selecting Session and default session will get loaded as selected in the last login with password or system default
The best practice to over ride this is to set a password for the user you need to login
to do this use a GUI console or Virtual console
and use this command
]#passwd user1
Enter new password
and logout
to GUI (Ctrl+Alt+F7) from virtual console click on desired user
and up on password propmt there will be session selection option below to login button
there are altername options from Gnom to KDE and KDE to GNOMe
these are as below
From GNOME
========
]# startkde
KDE will load over GNOme
From KDE
======
]#gnome-session
GNOME will load over KDE
Editing configuration files for the same is different form Distro to distro
in Redhat the path is as below
/etc/sysconfig/desktop
One more option is there to change default desktop
install switchdesk
]#yum install switchdesk
(as root)
after installation use this to make default session
GNOME
]#switchdesk gnome
KDE
]#switchdesk kde
