Chances are the FAA uses proprietary software to create the diagrams, or it's entirely possible it's a mix between CAD software and Adobe Illustrator.
Your best bet is to find a copy of Adobe Illustrator or something like it where you can work in vector format.
You could also find AFCAD, which is a program used to design/edit airports for Microsoft Flight Simulator.
[Edited 2010-08-18 12:42:26]
I'd take the awe of understanding over the awe of ignorance any day.