Requirements for WPA
To join a WPA network, a Macintosh computer must have:
an AirPort or AirPort Extreme card (see Note)
Mac OS X 10.3 or later
AirPort software version 3.3 or later for the AirPort Card (available via Software Update)
AirPort software version 3.2 or later for the AirPort Extreme Card (available via Software Update)