Why dont you just plug his in via USB. My brothers pc used to get internet over USB through our twowire gateway modem. It was only about 230kb/s but that should be enough for any gaming.
Your modem should have come with a manual, cable, and CD that tells you how. If not, you might try looking on your ISP/modem's site for the software. If still not, your going to need to get a couple of
network cables and
a switch.
Modem<network cable>switch<network cable>two computers
Hope this helps
.