Shared key authentication in iwconfig?

Hi. I own a Atmel USB 503A based adaptor manufactured by Prime
Electronics. I've been able to make it work fine without and with
encription.

I'd like to know how to activate shared key authentication when enabling
WEP.

After some googling, I learned iwconfig doesn't support enabling shared
key authentication (it may be changed by now though). If that's true,
how could I do it? So far the only way I've been able to do it is
through lvnet, which is not viable for an automatic script based
configuration process.

Thank you in advance for any hint.

Elder.