Why is my iBook G4 not WPA capable?

I try to set a password for my network so I won't provide free Internet for the whole neighborhood. But this pops up when I try to set a password.


Joining a WPA-protected network and making changes to a WPA-protected base station requires a WPA capable computer. This computer is not WPA capable. If you continue you will not be able to join the WPA-protected network or make changes to the WPA-protected base station.

What can I do?

iBook G4