Assuming you already have a phone line...
If you have broadband through your phone, from BT or Tiscali or someone, you want to get this:
http://www.ebuyer.com/product/52244
If you have broadband through a cable service, i.e., Virgin Media, then get this:
http://www.ebuyer.com/product/48546
That should come with the cables etc. that you need.
Regarding iBook: if it doesn't already have airport, then you'll need to go to an Apple store and get one (or perhaps online from somewhere else, but the prices probably won't be much different).
If you click Apple -> About this mac. Then click 'more info...', then see if there is 'airport card' mentioned in the 'network' section on the left of that window.