Deploying default Wifi settings and Passwords
I believe PackageMaker includes some first-run scripts, does it not? The easiest way is probably to make use of the networksetup command line tool in a script set to run on the first launch of an image.

To add a WPA network:

networksetup -addpreferredwirelessnetworkatindex AirPort mynetworkSSID 0 WPA superSecretPassword


The encryption type can be one of:


OPEN — open hotspot, no passphrase necessary of course.
WPA
WPAE (WPA Enterprise)
WPA2
WPA2E (WPA2 Enterprise)
WEP
8021XWEP (802.1X WEP)