Freeradius, wireless access point and password authentication

[Roberto]

I had a fast look at the authentication gateway howto... Sorry, I do not 
understand how can it help me...
I want to find a means to authenticate the wireless clients towards the 
access point, not towards the rest of the - wired - network.
The wireless client must not be able to associate to the AP, unless it 
supplies the correct credentials: that way, only authenticated users can 
associate to the AP and mutually 'see' themselves. Certificates are very 
good for this, but are not so practical when clients belongs to 
occasional customers...