XDMCP Issue
 

Running FC3, I can login remotely with XDMCP fine but I can only do so if I start "gdm" on the remote machine which then always starts X.

I don't know why I have to do this, also got an FC4 box and there I don't need to do so.

Even if I boot in init 5 while running KDE I still need to start gdm before I can connect remotely.
Then it tries to start a second dispaly and complains about a display already running.

Any clues on how to resolve this?

Cheers

1. setup KDM, not GDM since you are using KDE. Make sure whatever DM you are using is started by init. You always need some sort of DM. You could use XDM if you really don't think you will use any features of KDM or GDM.
2. Is the command you are using to bring up the remote computer "X -query hostname"?

Make sure you read the XDMCP-Howto, no matter what you do.