Have you run Software Update recently? Make sure your Airport software is up to date.
Does your iBook "see" the base station? When you click on the Airport icon in your menu bar, does a "Apple Network xxxxxx" appear in the list?
Have you run the Airport Setup Assistant? Once you establish communications with the base station, then you run the Airport Admin Utility (in you Utilites folder) to manage your base station (password, security, etc.)
If you still have problems after that, call Apple. They will walk you through it if you are still in the 90 days of free tech support or you bought Applecare.
I know when I got my Extreme base station, there was a firmware update that I needed for it to work.
Let us know how it works out?