I gave away my last 802.11b Airport-equipped Powerbook a while back, but I'm *positive* that they do support WPA (not WPA2) with TKIP (Not AES). WPA+TKIP is a vast improvement over WEP, so if you can provide that instead you should be good to go.

(You might find warnings that WPA+TKIP has been "broken", but the exploit in question is basically limited to DoS attacks. It doesn't allow someone to meaningfully join your network or listen to (real) data traffic. Unlike WEP, which is trivially broken wide open.)