I finally did figure out how to set the background with gdm.

1) The configuration files for gdm are installed in /usr/X11R6/etc/gdm
2) I edited /usr/X11R6/etc/gdm/Init/Default to set the background. For 
example:

#!/bin/sh

/usr/X11R6/bin/xsetroot -solid "#cccccc"

Sets  a solid light-gray background instead of the default green background.

I can also display images using wmsetbg or xii:

/usr/X11R6/bin/wmsetbg <image file>

or

/usr/X11R6/bin/xli -fullscreen -onroot <image file>

Hope this is useful to anyone else!

Taro

Taro Fukunaga wrote:

> Jan,
>
> Thanks for your suggestions, but it doesn't work. According to the 
> documentation for gdm:
>
> "The configuration files for GDM are located in the etc/gdm/ directory.
> ...
> Use the Init/* script for programs that are supposed to run alongside 
> with the GDM login window. xconsole for instance. Commands to set the 
> background etc. goes in this file too."
>
> I made a file called script and placed it under the Init directory, 
> but this script is not being read. It just says
>
> xsetroot -bg gray
>
> Since I don't see how the BSD daemon is being displayed by gdm, I 
> guess it is hardcoded? This is bad, when I do a make install the 
> install script should create a directory called /etc/gdm with all the 
> configuration variables and files. But I had to create these 
> directories manually although this is the first time I am using gdm on 
> this computer.
>
> Actually I only found the documentation for gdm after untarring the 
> tarball and searching through the docs directory, since man gdm gives 
> me nothing.
>
> So much for gdm-2.2.0! It should be 0.9 or something : )
>
> Taro
>
> Jan Schaumann wrote:
>
>> Taro Fukunaga <tarozax404@earthlink.net> wrote:
>>
>>> How do I configure gdm's background? I read the README but I don't 
>>> find a property to do this.
>>>
>>
>> gdmconfig
>>
>> Also, see /usr/pkg/share/gnome/help/gdm/C/index.html and look at the
>> various files in /usr/pkg/etc/gdm/
>> -Jan
>>
>
>
>