There are a couple of ways of doing this. As GTK+ allows
the appearance of applications to be changed at run time using
resources you can use something like the following in the
font = "-adobe-helvetica-medium-r-normal--*-100-*-*-*-*-*-*"
Another way to do this is to load a font within your
program, and then use this in the functions for adding text to
the text widget. You can load a font using, for example:
font = gdk_font_load("-adobe-helvetica-medium-r-normal--*-140-*-*-*-*-*-*");