Whenever I “su” to work as root and start an X application I get thoese “Can’t connect to X!” errors. This happens because the X-Server is run by the respective user. To avoid this problem you can “forward” the Xauthority from the user to root.
Use this snippet in roots .bashrc:
if [ -n "$DISPLAY" ]; then export XAUTHORITY="/home/<username>/.Xauthority"; export DISPLAY=":0.0"; fi