First we need to install Sounds for Gnome, such as gnome-audio-2.22.2-4.fc11.noarch and ascertain login.wav is stored in the directory /usr/share/sounds.
Second we go to System>Preferences>Personal>Startup Applications>Startup Programs, select Gnome Login Sound, and edit its command.
The initial state is given below.
/usr/bin/canberra-gtk-play --id="desktop-login" --description="GNOME Login"
It needs to be modified as given below.
/usr/bin/canberra-gtk-play -f /usr/share/sounds/login.wav --description="GNOME Login"
Third we can hear login.wav instead of desktop-login.ogg when we login again.
Finally I will be happy to assist you in customizing the login sound on Fedora 11.