i installed both the KDE and GNOME desktops so i can choose which one i like better, but i can only load the one that was installed as the default. if i want to view the other i have to reinstall it as the default. If i do KDE then GNOME won't even load and if I do GNOME, KDE goes through the load and the progress goes to 100% then goes to a gray screen w/ a mouse...i can still logout after that.
Use the switchdesktop application; if in GNOME run switchdesk-gnome, if in KDE run switchdesk-kde. This will allow you to change the default desktop.