Your iBook does not have PCMCIA. It's a card slot mostly found on laptops (e.g. PowerBook).
Yes, your iBook does have an ethernet card.
For sharing your DSL connection with PC and iBook you are going to need a router. You could build one yourself by using an old PC and run Linux, but it's a hassle. Hence, it is much easier to buy a DSL router. A lot of companies produces routers. Netgear (
www.netgear.com) is very good, IMO.
Another option would be to get an AirPort 2 Base Station. It has DSL routing built-in and you can connect your PC and iBook to it.
The AirPort 2 and AirPort Extreme Base Stations are Windows compatible so you could connect your PC to it as well, but if it's a desktop PC connecting it via wireless LAN is too expensive, in my eyes.
I think a DSL router is the best solution for your problem.