In their usual efficient way they promptly repaired it and sent it back (still under warranty so there was no charge). Now I have wireless access once again.
It feels like having a whole new machine. I really, really missed not being able to surf the web wirelessly and hang out at local hotspots. The airport card may seem like a relatively minor part of an iBook but when it wasn’t working I missed it more than I missed my CD tray when that broke on my old iBook.