I agree with Grumpy, you'll need to connect your connection from the Cable Modem to the up link port of a router. Then you can connect the 3 PCs to the other ports. You need to follow the instruction on how to setup a home network. There is a plethora of info on the web that will step you through this process.
You were right, Grumpy9117. My cable ISP was giving 2 IPs by default. The extra one was required to run 3 connections to a hub. After weighing things, I might opt for a router+upping the speed of the connection later.
Agreed, check out newegg.com, or tigerdirect.com, you should be able to find a decent router pretty cheap that has some switch functionality built into it. If you get a router to hide everything else behind, all your ISP will see, or should see anyway is just one IP address, so no extra monthly charges. Even with a wireless router, most of the time they come with some kind of switch/hub functionality.
I have a wireless router similar to this at home, works decently for connecting my main pc to the internet, as well as giving my laptop connectivity via wireless. Also has 4 ports so you can hook up with wires the same as you are now, and then gives you that wireless for later. So it works decently. Plus it should hide your other machines behind it, so the ISP thinks you are only connecting with 1 pc. Hope it helps you out. Btw, I think it also has a little firewall functionality built in, but I'd still run software firewalls on my pc's if I were you, as well as antivirus, I reccomend AVG antivirus myself, as it's free, free updates, works ok for my needs.