I'm in the process of trying to make a python script to generate Postnet codes, largely because I can't get the barcode generator to work.
Aside from that, when goes to the barcodewriter site, one can certainly generate codes, but they don't meet the criteria published by the US Postal service: http://pe.usps.gov/cpim/ftp/pubs/Pub25/pub25.pdf (see Chapter 4, page 39) which have very narrow ranges for various parameters, eg, the long lines can be 0.115 inches to 0.135 inches in length, and they can be 0.015 to 0.025 inches in width. So right now, trying to work through Scripter to generate lines right on the page instead of image files. Greg
