By your post, I am assuming you know the differences between WEP and WPA. Nevertheless, I do not know your answer. But what I can say is, WEP is better than not having any security.
I just bought a powerbook G3 which has an airport card that only allows for WEP. Did they ever make a WPA airport card that can be installed in my 800 Mhz I-Book, or am i stuck with an insecure wireless network?