I would suggest 10.2 at a minimum, 10.3.x in preference.
It's entirely possible that there is some way of setting up a PPP link like the one described under OS 9, but I would have no idea how you go about that. Another option (if that ethernet card doesn't turn up) is to install linux on some other hardware, like a spare x86 box or suchlike.
In fact ... and this would be the long way around to be sure, you could try installing linux on the iBook and running OS 9 inside MacOnLinux