If you have installed openSUSE with the default selections of choosing one of the available (say KDE4) then only the selected Desktop environment is installed. However, should you later choose to install and use another desktop Environment say (GNOME) then this can easily be installed and as always just a few clicks away.
To install GNOME Desktop Environment from a system where there is a KDE4 Desktop environment is installed (as in my case) then
1. From KMenu, click Computer – Install Software
2. Set the Filter type as “pattern” and under Graphical Environment check the box for “GNOME Desktop Environmnt”. This will automatically select the GNOME Base system. Now, click Accept.
3. This will bring up a list of dependencies that needs to be installed, click Accept.
4. This should install the desktop environment. Once installed, you can simply logout and select “GNOME” under the “Session Type” to use the GNOME Desktop environment. openSUSE will remember the last used session so the next time, it will default to the newly changed GNOME desktop.
The above procedure can be used to swap from GNOME to XFCE or XFCE or KDE4 or ofcourse any of the combination.