OK, now I have the xorg.conf file on the run I'm left with the xdm error.
There is an error in the xdm.log file:-
xdm error (pid 7439): XDMCP socket creation failed, errno 97
A Google search hasn't brought up much but the one thing that's possible is that xdm is expecting IPV6 and I don't have IPV6, this seems odd as I've installed a well debugged distribution.
Any ideas anyone?