I wanted a way to automatically set up a printer without having to touch the machine and after much work, I did it (with a little help from some friends). Here are the steps I used in order to get it to work. Your mileage may vary, and this isn't a post action, since some of the commands aren't included on a default NetBoot image. You'll need Mike Bombich's excellent NetRestore
First, log into NetRestore's PHP services, and go to Database administration » Create Machine Specific Attributes. Add these specific field names (spelling and case counts!). The following is laid out in this order: field name | Data type | Default value (if any)...
Go to this URL...
http://your.netrestore.sever/nr/nr_machine_settings.php?hw=00:00:00:00:00:00
replace 00:00:00:00:00:00 with your machine's MAC address. Enter in the data for that machine for the fields you just created. Spaces aren't allowed in the printer_name, printer_location, or printer_address fields. They are allowed in the printer_driver field. For the printer_driver field, find the right file name by going to /Library » Printers » PPDs » Contents » Resources » en.lproj. You'll find the correct printer driver in that folder. For example, the one I needed to add was called HP LaserJet 4200 Series.gz.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20070504130353517