The default desktop option problem continued till FC3 in RedHat series of Linux is that even though if you change your desktop to kde, next time when you reboot it will load gnome instead of your settings. Some times this may not happens.
Solution for this is to create a file named ‘.dmrc’ in home directory and the following content to that file.
[Desktop]
Session=kde
If you need gnome as default, change ‘Session=gnome’ instead of above.