Hi, and welcome to Apple Support Communities.
Which exact iBook model is it?
You can choose from this list:
Which version of the operating system is it running now?
How much RAM is installed?
What kind of optical drive does it have? (CD-ROM, CD-RW, DVD, Combo, or SuperDrive?)
How do you connect to the internet? Do you have a wireless cable modem or wireless router? DSL?
Note, if your iBook is not Extreme compatible, hooking up a WiFi bridge ethernet router with LAN ports via ethernet is much more preferable, because the security of the original Airport card/base stations leaves much to be desired and so does the speed of the network. Also, pre-September 2003 Macs do not include USB 2, so USB adapters will be just as slow as the original airport card, and much slower than ethernet. And that's even if you can find the corresponding drivers for the operating system. A good router with an up to date firmware helps, if it is knowledgeable about your operating system. Pre-Extreme Airport cards could only hook up at 11 Mbps and only encrypt WEP or WPA1.