network with cable modem

A Broadband Cable/DSL router is the best option for you because it provides firewall (in the form of NAT). These also provide ports for 4 or more computers (simultaneous connections to the Internet without having to use one computer as a gateway).

I use this and recommend it:
http://www.linksys.com/Products/product.asp?grid=34&scid=29&prid=20

(no affiliation with LinkSys ; just a personal recommendation).

first question: are you on AOL? if so, write back for further info as only certain devices will work for you...
you need a device that will allow the single public IP address assigned to you by your ISP (the WAN ip address of the cable modem) to be shared by all the computers on your network. the device that let's you do that is not a hub or a switch, but a router. a switch will work (connected between your cable modem and the rest of the computers) but only one pc at at time can use the internet...i believe what anna777 (correctly) spec'd is a cable modem with router. the NAT (network address translation) capability of a router is what lets you all share the same IP address, let's you all be on the internet at the same time...if you already have your cable modem, you can just buy a simple router and hook it up. the NAT will give you protection but imho it is not a firewall...
the other hardware you'll need is a cat5 or cat6 rj45 twisted pair ethernet cable for each pc (long enoughto reach from each pc back to the router) and a network adapter on each pc (with a rj45 connector). don't sweat it if you only have 10mb network cards, they are fast enough...
maybe you want wireless instead of cables? this might work for you if the home network pc's are within 'radio' sight of each other...not a sure thing at all...and more expensive as each pc will need a wireless ethernet adapter instead of inexpensive plain cabled network adapter...
i would add a software firewall on eachpc, i like tiny firewall (www.tinysoftware.com). i do not like zonealarm but lots of folks do...i use it at home but i don't like it. i don't use it at work.
probably the company that provides your cable internet has a software firewall recommendation...why not go with that...

For the first time I have a difference of opinion with Anna777. You should check out http://www.netgear.com/products/routers/comparisonchart.asp too. I recently replaced my NetGear RT311 with a NetGear RP614. Either way, you are looking at well under $100.

The issue becomes what will your ISP let you get away with. Most allow sharing the single IP address via NAT router but offer no support if you have problems.