So, what I'm getting is that you are using win98 as a GATEWAY? so your cable connection is internal?
If it is, I would say: "UPGRADE A.S.A.P!!!!!!" If you have a cable modem that stands between your 98 box and the internet, simply point your linux mahines to it through a switch or a hub. Then, you won't need the 98 box as a gateway anymore.
If you want a gateway for security reasons, Might I suggest IPCOP? It's a Linux firewall distro that works VERY well. Just throw it on an old box with 2 NICs and go. Pretty easy to configure. If you decide to go that route, and you need help e-mail me, or check out the forums at
http://www.ipcops.com. You can get IPCOP from either ipcops.com or
http://www.ipcop.org (which is the official site, by the way).
Well, with that information, That'a all I can do