If your W98 is Second Edition you can use the W98 Internet Connection Sharing to share a connection, but you have to work a lot to get it to run with a broadband connection vs. a modem.
You can configure your linux box to be a NAT router to share your broadband.
IMHO, the best solution is get an external DSL router like a Linksys. You can get one for under $50.00 US these days.