The code linked from this node simulates the behavior of a Perl hash, and then draws a picture of the resulting data structure. Here is an example output, demonstrating the layout of the following hash:
%h = ( When => 1, in => 2, the => 3, course => 4, of => 5, human => 6, events => 7, it => 8, becomes => 9, necessary => 10, for => 11, one => 12, people => 13, );
If you ask Perl to print out the keys in this hash with keys %h, you get the following list: (becomes necessary human people course in one When events of the is for), which as you can see is the order that the keys actually appear in the hash structure in the illustration.

Right now the module emits pic code, which tells the Unix pic program how to draw the diagram. pic is a little obscure. But I designed it so that it will be easy to subclass it and override a few methods (draw_start, draw_end, draw_bucket, draw_node) so that it renders the diagram in PostScript or with GD or whatever you prefer. Contributions will be welcome. Complete documentation is included, of course.

I didn't want to post the source code here because it was about 450 lines long.