The original AirPort card can not do WPA or WPA2 networking, especially in Mac OS 9.

Your best best is to either run a passwordless network, or a network with WEP, or (even better) use a more modern device as a bridge -- there are bridges designed for gaming consoles which you can set up to use WPA2 security, or you can set up an old router as a bridge.

The advantage to this is that you can join non-wireless Macs and other devices to your home network, and if you get one of these devices designed for operation on a G network, you will not experience performance degradation, which can sometimes happen when joining wifi devices using an older standard to a newer type of network.