Can't say I've ever heard of a "Netscape router", but anyway...
When you say "the router allows access to the web based setup/maintainace page and nothing else", I assume that means that, with the airport card connected to the iBook and the airport-extreme connected to the router, that you can access the router's web-config pages? If so, then the wireless-part is working fine......it also means your IP-addressing "should" also be fine on the iBook.
Next thing to check, does the router have its own built-in ADSL-modem, or are you connecting a PC with an ADSL-modem to the router to supply a connection to the rest of your network? If the latter option, then you'll need to configure the PC to share the connection and the iBook to use the PC (and not the router) as a gateway to the internet. If the former option, then it "should" all work fine.
If the router does have its own built-in modem, and you can connect fine with the PC, then just need to run a few tests on the iBook. I've never used one, but if it's new, I'm going to assume it's running Mac OS X......if so, fire up the terminal (from memory, Go -> Utilities (may need to go into "Applications" first). This will give you a Unix-like command-line interface. Now, Wanadoo should have given you some numeric (IP) addresses for their DNS servers, which we will use as a test here (if they didn't, just use 212.58.224.113 instead - BBC's website).
Basically, at that command-prompt, type in the following: ping 212.58.224.113 (swap for Wanadoo's own DNS server's, if you have the addresses)
After pressing return, you should see something along the lines of the following (press Ctrl-C to stop it running):
PING 212.58.224.113 (212.58.224.113): 56 data bytes
64 bytes from 212.58.224.113: icmp_seq=0 ttl=249 time=21.823 ms
64 bytes from 212.58.224.113: icmp_seq=1 ttl=249 time=22.425 ms
64 bytes from 212.58.224.113: icmp_seq=2 ttl=249 time=22.299 ms
If you do see the above, then I'd say it's a DNS issue on the iBook, as connectivity to the outside world would seem to be working fine. If it does work, try the following: ping
www.bbc.co.uk
If you get the following, it's definitely a DNS issue:
To fix that, you'll need to go into the network-properties in your System Properties, and manually add Wanadoo's DNS servers into the relevant section (if you don't have them, you'll need to ask Wanadoo for them - they normally come in pairs).