Just an update:
There is a relatively new attack on WEP; an article about it is at
http://www.tomsnetworking.com/Sections-article111.php
Basically one tricks the access point into generating the traffic that's required to collect the large amount of data required to crack a WEP key.
The attacker used to have to wait until sufficient traffic was captured. With this attack, he can generate the traffic himself.
It's only a matter of time before a simple utility appears that cracks anybody's WEP access point; usually in minutes.
Suppressing SSID broadcast will be a first line of defence - assuming the network isn't in use at the time he is driving by, and he can't guess the SSID. So "linksys" won't hack it
WPA is a must.