Hey there so here is what you need to do:
Network Diagram just for you!
1) Buy a router
, unless like previous poster said your ADSL modem has built in router, which the new ones from service providers usually come with now. if not you can go to D-Link
. Now I use both so it doesn't really matter. I would recommend (depending what country you are in) to purchase something like the D-Link DI-524
which is a 4 port wired/wireless router.
Once you have figured out if you need the router or not... you need to place the router after you ADSL modem, you may also need to register your MAC ID - that depends on your Internet Service Provider.
Plug each PC into the router, in any port 1-4. There will be 1 port called WAN which is where you modem plugs into - this port supplies the internet.
Each computer should detect the network automatically as they are set to DHCP by default.
Your finished, each computer should have the internet. Now there are a few more steps to get the system just right, like setting each Windows box workgroup, you should do this for any Linux services as well, like Samba.
If you want some more help just PM me or e-mail me (click the link)
and I will be glad to help!