Description of problem: The current kdebase4 package does not provide a kde4.desktop file (like kdebase-3 does provide a kde.desktop file). As a result there is no option in gdm or kdm to switch to a KDE 4 session. How reproducible: Try to start a KDE 4 session from the login. Actual results: It is impossible, although it should be possible.
It is not expected to be possible, there is no kdebase4-workspace package and there probably won't be one before Fedora 9. We're only packaging the development platform right now.