I successfully did this.
My setup was a single computer with a Speed Touch USB modem, connected to BellSouth Fast Access DSL.
I got another computer, got the D-link network kit (the 910e or something or other, the 100 mps one that includes a 5 port switch) and hooked them together. Got the networking portion up and running (standard Win98SE stuff). Fairly easy.
Once that was working, I tried the built in ICS in Win98SE, but I just couldn't get it to work out right, so I ended up going to www.sygate.com and downloading the "Sygate Home Network" product. It was recommended on this site.
Installation was a breeze, and now everything works perfectly. I am going to be adding a third computer soon. I also downloaded and installed their free (personal use) firewall softare.
I am very happy overall, and once I get the third computer up and running, and the whole shebang working properly, I am going to actually pay for the Sygate program.