Cynthetiq just helped me with this not two weeks ago. I connected a four-year old Gateway running win98 to an OS X PowerBook. I'll alert him to this thread, and see if he has anything to add.
(this assumes that both computers have ethernet ports. And you don't need ethernet crossover cables, just two regular ones.)
First, I used a hub - any hub will do, I used one similar to
this one but I'm sure someone else around here could direct you towards a reliable/cheap one.
I took my ethernet line to the internet and plugged that into the uplink port of the hub (to give both internet access - I don't think this is absolutely necessary), then I plugged both the win98 machine and the PB into the hub as well.
Then, I followed
these instructions, and they worked perfectly.
Good luck....post and let us know how it goes...