I've the same problem with YDL 3.0.1 on iMac G4 15'' Flat Panel. For example when I make "mplayer -vo xv /dev/dvd" (/dev/dvd exists in my installation) then I got an X crash and the system goes to the login-screen. The same happens with xine.
I can run mplayer with the x11-output but no chance of watching a DVD in fullscreen-mode.
In the meantime I googled around a lot, but I didn't find a solution, so help is welcome!