There is a book by O'Reilly "Perl Graphics Programming", if you want something to read. Perl has modules that interface to GD, to Image::Magick and even gimp and opengl. There are SVG or Flash/SWF, both might have some advantages if you want to look at it in a browser. And there is the all-in-one package of GraphViz, also usable through a perl module. I used GraphViz for a project and it was nice, but you don't have much input about the placement of the nodes