well you can try the simple setup like this:
I have no idea if your broadband comes with the need to connect over ethernet...
if it does its quite simple, I used to do it with a Pentium2 + Blue&WhiteG3 + trough Airport my PowerBookG4
so what do you do?
you buy a wireless router/hub with some ethernet ports and an antenna for the wireless function.
then you connect your pc and configure the router to your broadband, than you can surf the net with your pc trough the router wich is connected by a ethernet cable to the router, the next step is to configure your router to go wireless, and configure your PowerBook to connect trough airport to the router, and you can surf with both of them trough the same broadband connection...
just check for an ideal location for your router so the signal gets to all the locations where you want to use your PowerBook
greetings Jo