Hmmm, that doesn't sound right. If your ISP's settings were already set up on your iBook before the Ethernet port was damaged, then they'd still be on there. Try plugging everything in and see if it works.
If your ISP wasn't set up on the iBook previous to your Ethernet becoming unusable, just plug everything in, fire up the AirPort Admin Utility, and enter the settings manually as provided by your ISP.
The reason it probably wants you to set things up by Ethernet first is so that the AirPort connection can be auto-configured. I seem to remember that there was an option on the AirPort Setup Assistant for "don't have ISP" or "set up ISP later". In any case, if you can get the iBook to properly connect to the base station, and have the base station properly wired to your cable/DSL/phone line or whatever you use for access, you should be able to make it work.
