The list of features for Classifieds is pretty explicit and in the PhotoPost Classifieds thread I specifically state that the zip code is not a feature included. Keep in mind, viperalley is an active community site - not a "demo" site.
http://www.photopostdev.com/classifieds has a non-altered version which is more of a "demo" which you can play with, but ViperAlley is shown as an example of an integration being used (like a "Site In Action").
My understanding is you are talking to Scott about this, so I'll leave it to you two.