Setting up modem to share net through switch

A simple one for you guys:

How does one go about sharing an internet connection between 2 PCs on a modem and separate switch? I don't know the details of either because I'm asking for a friend, but it's a D-Link ASDL modem and a Belkin switch.

I assume the modem's ethernet cable goes into one port and the two computers in another two... but where does it go from here? I'm guessing they have to access the modem's menu and enable NAT of some kind.

Could anyone give a quick step-by-step runthrough that I can talk them through over the phone?

Cheers.

>>7
One of the computers will actually be connected to the internet through the ADSL modem and act as a gateway to the other computers if it's set up properly.  You'll probably need a second network card to attach the modem directly to the gateway computer, but they're cheap and easy to install.