It is possible to plug a 4 port switch into an ADSL modem (not a router) and connect the NIC of each computer to that switch, and connect each computer to the internet by using software like RasPPPoE like Ragerunner does.
What happens is that as each computer connects, it is assigned its own external IP address (so the ISP is supplying two or more IP addresses to one user). This is only possible if the ISP allows it (iiNet, Netspace, and a few other ISPs allow you to have up to 4 IP addresses for free whenever you're unshaped i.e. under your download limit), and this is known as multiple PPPoE logins and is quite different from using a router.
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Anyway back to the original topic about babydoll's cable internet sharing, your best option is to buy a router such as this one from Harris Tech:
http://www.ht.com.au/Scripts/xworks.exe?PART:A0203#Tof
You willl also need 3 ethernet cables in total (one for modem -> router, one for router -> computer1, one for router -> computer2)