2004-03-02 Fedora Tips 48:
With RH9, letting another system access the X desktop just needs xhost +othersys. But the Fedora Core xserver doesn't listen on tcp port 6000 so othersys can't open the display.
In Fedora gdm.conf, "DisallowTCP=true" is commented out, but it's true by default anyway! Setting "DisallowTCP=false" solves the problem. - submitted by David Wood