To share a broadband connection to a local area network, you need a switch which is also called Hub.
This switches are coming with 8 ports or 16 ports, depends upon the number of systems you can install the switch or hub.
Connect the main server to the hub through lan cable. Now connect the other computers from the switch or hub through separate lan cable.
Now setup each computer connected to the hub. First note the IP address of the server where the broadband connection is connected directly.
Now in each computer in the local area network,
b. click tools > internet optionss
c. click connections tab and click lan settings.
d. Now type the ip address of server for configuration.
e. If you don't have ip address of server, check for automatic detect settings.
Thus you will configure each system in the network to connect to a server of broadband connection.
a.If you are using a modem where the internet broadband connection is terminated on that modem then you can directly connect that modem in to the switch of your local area connection through an Ethernet cable.
b.Further you need to check certain things like what is the ip address of the modem and what are the DNS used by the service provider.Here there will be two ip address on the modem first will be the modems ip address already configured and second you will have to assign which will be in the range your local area connection.
c.Then you need to check if each computer in the network is able to ping that ip address of the modem which you have assigned to the modem.
d.Now if you find proper connectivity then you need only do is set each computer's gate way as the ip address of that modem and also assign the DNS addresses in the DNS fields.
E.you will be able to connect each computer directly to the Internet ,but to find the DNS of the service provider you need to search it on net or you need to first connect the internet modem directly to only one PC and in the command prompt type
"ipconfig /all " and note down the DNS addresses.
f.No setting is required in the internet options of the browser set it to default that it "Automatic detect" or "no proxy"
Second method is somewhat simple
a.Here you have to connect the modem directly to only one PC which i think is already the same in your case.
b.Then download a software which is free on internet called "Analog Proxy" and installed it on that PC.
c.Next you will see a red "P" symbol on the right hand below corner of your screen,click open it and turn on the HTTP service.Now the status of the P should turned Green.
c.now you need to just note down the Ip address of that PC and set it on each browser of the PC's in the network with the Port setting as 6588 which is port address the analog proxy uses.
that's all you should be able to browse internet on the pc's in the network.
Or you can use another software named ddproxy_0_05.exe whose port will be 80 and is better than analog proxy.