Don't think that's gonna work as you want it to anytime soon ... but if you have an old Pentium-class machine around, you can fit it with a network card, set up the Direcway Internet via USB and use 98SE's Internet Connection Sharing to pass access on to the SME server, which then in turn could share with the rest of the network. A bit kludgy but still offers you all the firewalling, etc. of SME.
You'd have to put some effort into securing the 98SE box, mostly by removing everything not absolutely necessary ... don't forget to zap the Personal Web Server!