I'm in the same boat you are. I've got a 5600 with OZ3.5.4 and want to get WPA working, but have no idea where to start. Can you slap a detailed list of the steps you've taken so far, so I can see if I can come up with the next steps? Also, is the wpa gui available via the feeds? If so, you theoretically should be able to just do
# ipkg install wpa-gui
And it pull the dependencies, including x11. Theoretically. I dunno if it'll do that drastic of a job of meeting dependencies, though..