I feel certain that Ziegler's Fig. 2.1 below (to which I assume you are referring?) was just drawn "by hand" in a generic drawing program, such as Adobe Illustrator, or xfig.
           Fig. 2.1 http://cs.smith.edu/%7Eorourke/MathOverflow/Ziegler.Fig2.1.jpg
           _{(p.643 = 27th page of notes linked by Camilo)}

This is probably not what you want, but Mathematica (via Combinatorica) can draw Hasse diagrams. See, e.g., this link for how to accomplish this.
                      alt text http://cs.smith.edu/%7Eorourke/MathOverflow/HasseDiagram.jpg

I feel certain that Ziegler's Fig. 2.1 below (to which I assume you are referring?) was just drawn "by hand" in a generic drawing program, such as Adobe Illustrator, or xfig.
          
           _{(p.643 = 27th page of notes linked by Camilo)}

This is probably not what you want, but Mathematica (via Combinatorica) can draw Hasse diagrams. See, e.g., this link for how to accomplish this.