My problem is the following: if I started kdm as user X and change to user Y I have to use xhost + to be able to start xclock. (xhost +localhost and the like is not enough.) But anyhow, I want to allow it for the all users on the same machine permanently. I tried to put localhost into /etc/kde2/kdm/Xaccess, /etc/X11/X0.hosts to no avail.