Welp, if you've put it on a Mac, it's stored and you can't get it. But my question is, how'd you get it in the first place? Obviously someone wold you what the key was to got onto the network with your iBook in the first place. So I would suggest that you just ask whomever told you, or find the piece of paper that it was on.
Will running some searches on this topic, I came across this site and thought you might like it:
http://www.ibookzone.com/linksys.shtml
Hope this helps...sorry if it doesn't
...necronom...