GTK programs (Gimp and Gnomecal) without X display?

[Bo Brinkman <brinkman cs princeton edu>]

I'm sure this has been answered, but I couldn't find an easy way to
search the archive. I searched the web, read the GTK+ faq, and the gimp
faq with no results..

How can I run GTK+ programs from the command line without a display? I
want to use the command-line version Gnomecal, and the batch mode of
Gimp in cron jobs, but I can't make it work. It just says:

Gtk-WARNING **: cannot open display: 

and then exits without doing anything. Sorry if the correct answer is
RTFM... I just haven't found the appropriate resource yet. :(

-- 
William "Bo" Brinkman                         brinkman@cs.princeton.edu
Princeton Computer Science        http://www.cs.princeton.edu/~brinkman
-- 
When ideas fail, words come in very handy. --Goethe