I'm using a Pretec CF WLAN card on OZ 3.5.1 (SL-5500, 64/0) with OPIE 1.1.6 and it works perfectly, usually without any additional configuration. It binds to eth0, and I've been leaving the networking set to 'any', and it associates right away with the access point (at which point the light on the card stops flashing and remains on). I've only used it with non-WEP APs so far.
Can you give more information on what happens when you try to use it? BTW, I've found that it seems to work best to power on the Z, plug in the card, then start Network... otherwise, go into the eth0 configuration menu, re-scan the neighborhood, and see if it will re-configure the setup automatically.