If the ADSL modem comes with an Ethernet port and a USB port you could connect one with Ethernet and the other with USB, but as the others said it would be better to get a ADSL router. This would replace your modem. The difference that you would see is that it is much like the modem but with more Ethernet ports, and some have wireless too. there are some more complicated hardware and software inside the router but you don’t need to know about this, its magic.

2 ways

get a router – the simpliest

or add another PCI network card and get a crossover cable or a hub and 2 patch cables and connect that the second and share the connection coming into the 1st computer – can be done cheaply

the first way doesnt need the 1st computer on for the 2nd to be able to access the internet

the 2nd way requires the 1st computer be on for the 2nd computer to be able to get online.

You can share an ADSL connection on one computer with another, but it’s a lot easier to pay $30 for an ADSL router and use that.

The router sits between your ADSL modem and your computers. One cable leads from the router to the modem, and one cable connects each of your computers to the router. The router handles everything involved in setting up the connection, and then your other computers can share it. You only have to enter a few configuration parameters (your user ID for the ADSL connection, etc.), and you’re set to go.

This is much more efficient and straightforward than trying to share the connection one computer has with another computer.