hi fren

i abit blur for your setting ; LAN cable --> Macbook ---> Airport Extreme

it should be ADSL Modem > Airport extreme > macbook

Airport extreme itself already a wireless router and 4port hub. not macbook as hub..after setting u can even unplug the lan cable from yr macbook, just leave the modem and airport extreme ON and you can enjoy the wifi at home within the range.

Security wise try use WPA/WPA2 in-seat of WEP, i can't use WEP on my office setting, PC use b/g cant connect until i change to WPA.

Try reset the airport extreme b4 re configue anything.