As above:
You only need to configure the wlan0 interface.
I'm still not convinced that the opie or gpe interfaces actually properly save wifi settings, but I've yet to have this proved or disproved one way or the other.
The safest bet is to configure everything via the command line using iwconfig, so get googling for that. Alternatively, if you don't want to get under the hood of iwconfig, search this forum for iwconfig as I've supplied numerous examples detailing it's use under OZ.
Once you're done configuring, use ifup wlan0
from the console.
Good luck