I generate most of our internal printing (invoices, labels, etc) in postscript. I have a customer who wants to do their labels in the same way. After some looking around I found this. WORKS REALLY SLICK!
http://www.terryburton.co.uk/barcodewriter/
From the web site:
Barcode Writer in Pure Postscript is an award-winning open source barcode maker, as used by NASA, that facilitates the printing of all major barcode symbologies entirely within level 2 PostScript, ideal for variable data printing. The complete process of generating printed barcodes is performed entirely within the printer (or print system) so that it is no longer the responsibility of your application or a library. There is no need for any barcode fonts and the flexibility offered by direct PostScript means you can avoid re-implementing barcode generator code, or migrating to new libraries, whenever your project language needs change.
It makes including any barcode within a PostScript document as simple as inserting the following directive:
50 450 moveto (1-86074-271) (includetext) isbn barcode