If you want to share a cable modem among multiple computers, you will need the network wiring (Cat5) a network card in each computer and some sort of sharing device.
I think the easiest approach is to purchase one of the Cable/DSL routers with a built-in network switch. My favorite is the Linksys but D-Link makes a credible product as well. These routers provide all the functions you need in one box for about $125-$200 and the LinkSys comes in both 4-port and 8-port models.
Alternately,if you're trying to do this at minimum cost, you can use Windows98SE or W2K on one of the workstations and use the built-in Internet Connection Sharing functionality. This workstation will require two network cards and you will have to purchase a separate hub or switch for the network function so you'll probably save $35-40 over the cost of a Cable/DSL router with a switch built-in.
Also, just for the record, what the cable company would prefer is that you plug the cable modem into a hub and lease an IP address from them for each additional computer (usually about $7 per month additional per computer). In my experience, if you don't use that option, they won't squawk too much about your home network as long as you don't expect them tosupport the network part of it. If you have any problems, they will usually ask you to bypass your Cable/DSL router for troubleshooting purposes and plug your workstation directly into the cable modem.
As far as Win98 versus W2K for the younger folks, my kids' ages are from 3 to 13 and they don't seem to notice much difference between the two. They do have some older hardware and software that seems to run better with Win98; on the other hand I prefer my ability to protect their desktop with W2K.
paul