Is it a 700MHz/800MHz model, or a 1GHz/1.25GHz model?
If the latter, just get an 802.11g Airport Extreme card off eBay and upgrade to 10.4.11 (or better still Leopard)...
If the former, the card is only 802.11b (11mbps) and does not support WPA2 (and WPA support is flakey). I'd suggest a wireless ethernet bridge in that case, because the USB ports are only version 1.1, rather than 2.0, meaning speeds will be, at best, 11mbps.