I have a similar set up at home.
I have 3 machines, Cable Internet from RoadRunner, a cable modem, and an SMC Barricade Broadband Router.
If you only have 4 machines, you can buy the cheaper 4 port SMC Barricade, and if you want to add more machines use a 10/100 switch, the SMC has auto-sensing uplink ports (there's a name for that feature...can't remember it right now), and you can add as many as 253 total.
The print server built into the SMC is very handy. For two reasons that I can see. 1. No system has to be on all the time to serve print jobs. 2. The SMC has a parallel (RS232?) port on the backside, so you don't have to have a network ready printer (usually reserved for Laser printers and some higher end Ink Jets).
To set the whole thing up, you simply plug the Cable Modem into the WAN port on the back of the SMC and then run one end of a cat5 patch cord into the SMC, and the other end into the NIC card on your system...set the network connection properties to Auto Configuration (basically that's it) and you're set.
There are a few nuances that need to be dealt with. You should configure the SMC to your liking, using the web interface this is easy...with newer models you surf to
http://192.168.2.1:88 and go...the first time you log in there is no password so you would want to set one and then configure to your liking.
When I signed up for cable internet I got a deal from Road Runner offering free setup and free hardware (cable modem and NIC) so I have the modem they supplied. It's a 3COM 'Home Connect' or similar, it offers cat5 and usb for ease of use. I haven't had any issues with it, but it's ugly...like a sharks fin, silvery with bright green lights. It's hidden behind my systems.
Hope that helps a bit..
-Dan