Some Alternatives:
If you want to use a linux machine both as a firewall/router and as a workstation you could follow the directions at: (How to set up ip masq) This is less secure but saves the cost for the 486. 

Another alternative is internet sharing on win98

A third alternative is the Linux Router Project A good place to start- but somewhat difficult to use.

there is LinuxHQ

If you know of other sites that should be here - send me email

From: "Shawn Furgason"
Share The Net is a similar product (Linux boot disk based), although commercial. It has a nice web based config tool and easily configurable for adding specific ports to grant/deny access.
You can check out the product at http://www.sharethenet.com