• Xnest

If you are in an existing X Windows session and would like to open a session on a remote computer that is also running the X server, you can simply use Xnest in the following way:

Xnest :1 -query (remote host)

The :1 defines the session number on the local machine (the local X session is usually :0).
The remote host is the 'contact named host for XDMCP', which is the X Display Manager Control Protocol. Here is a HOWTO on the subject.

• X Display Manager (xdm) Resources

Many xdm parameters can be set in:

/etc/X11/xdm/Xresources

If you have, for example an XConsole, you can alter its position and window state by modifying the follow values:

XConsole.text.geometry: 480x130
XConsole*iconic: false