System Architecture: Intel
RedHat Release: RHL 5.1 (Manhattan)
FAQ Category: X Windows
Modification Date: Oct 19, 1998

Question:

How do I change the XDM graphic displayed at login time?

Answer:

This is from some great recent postings on the redhat-list.

The graphic is in /etc/X11/xdm/Xsetup_0
        /usr/X11R6/bin/xbanner  -file 

Change the graphic via:
        /usr/X11R6/bin/xbanner -file 

For example:     
        /usr/X11R6/bin/xbanner -file 
               /usr/doc/xbanner-1.31/samples/Demo/FgPlasma
               -label `hostname`

Also, comment out the lines with rhpenguin.xpm in:
       /usr/X11/lib/X11/app-defaults/XBanner

References:

postings on the redhat-list last month