http://www.apple.com/support/downloads/airport41formacosx.html
AirPort 4.1 for Mac OS X
The AirPort 4.1 for Mac OS X 10.3 software supports all models of Apple AirPort base stations including the AirPort Extreme and AirPort Express models.
What's new in AirPort 4.1:
Supports Keyspan Express Remote for use with AirTunes (AirPort Express only)
Support for WPA security on WDS networks
Ability to rename a USB printer connected to a base station
This software update provides improved AirPort wireless networking software, and is recommended for all users with an AirPort Extreme and AirPort enabled computer or an AirPort Extreme or an AirPort Express base station.
AirPort 4.1 for Mac OS X
The AirPort 4.1 for Mac OS X 10.3 software supports all models of Apple AirPort base stations including the AirPort Extreme and AirPort Express models.
What's new in AirPort 4.1:
Supports Keyspan Express Remote for use with AirTunes (AirPort Express only)
Support for WPA security on WDS networks
Ability to rename a USB printer connected to a base station
This software update provides improved AirPort wireless networking software, and is recommended for all users with an AirPort Extreme and AirPort enabled computer or an AirPort Extreme or an AirPort Express base station.