A router is an excellent idea, just stay away from wireless routers, hackers can get within range and with a wireless card on laptop, use your I.P address, and even get on your computer that way. Although that problem isn't as prevelent in America as it is in the U.K. they call it Warchalking over there. You ought to look it up, its actually pretty interesting.
Actually a wireless router properly set up is one of the best defenses. I work for Comcast broadband and troubleshoot internet connection all day. (like right now) In a wireless router it has a smaller computer brain that holds configuration software and communicates constantly with any pc that you hook up to it. When you get it it is set up to just work, but none of the securities are turned on. Every wireless router has securities of some kind to stop unwanted PCs from getting into your network. For example, my SMC router has a MAC filter which uses a hardware address (pc fingerprint, no two are alike) to determine which computers you want on your network. They are very good. Routers, and wireless routers are the best type of firewall I know of and the first option for a firewall offered if you were to call in as a cutomer that we give.
Just so you all know.