Using Xcfbpmax and xdm from 
ftp://ftp.unit.no/pub/NetBSD/arch/pmax/X11R5/ver-5.26, I ran into quite a 
few problems:

1.) From the console (being logged in as root, of course), xdm can 
    sometimes not be started, but aborts telling that it can't 
    open/write/lock the pid file /var/run/xdm-pid. This never happened to 
    me when I started xdm from a pseudo terminal.

2.) I let xdm manage the local server running Xcfbpmax. It seems that 
    when entering username and password, only the left shift key of my 
    LK401 keyboard is working properly, not the right one. I guess this 
    can be cured with suitable xmodmap commands, but translations in the
    resource file might be more convenient. Does anybody happen to know 
    whether there is a way?

3.) It seems that if xdm is started managing the local display, there are 
    two xdm processes running on the system, the pid of the X server 
    surrounded by the pids of the xdm processes. Their status flags are 
    'I' for the smaller, and 'S' for the larger pid. After killing xdm by 
    hitting Ctrl-R on the login window, the 'I' xdm process remains. Is 
    this behaviour supposed to be correct? Why are there two xdm processes?

4.) Eventually, I'd like to end up with a system that presents the user 
    with a choice of xdm hosts (very much like the login selector of 
    NCDware). The local machine should not be a valid choice. Of course, 
    I could start xdm, not letting it manage :0, then start the X server and 
    connect it to xdm via -indirect localhost which seems to work. 
    However, I don't like that all hosts are asked whether they would be 
    willing to connect, and that a connection with an X11R4 xdm host 
    cannot be established at all. Does anyone know of any free X client 
    that would allow to present a passive choice of hosts, and eventually 
    submit an XDMCP query to the selected host in much the same way the 
    NCD chooser does?

Helge