You need a wireless router. If you don't have one, you can get them at staples, best buy, even walmart. I use a pretty cheap one, $35. It'll do the job, though.
http://www.amazon.com/Netgear-WGR614-Wireless-G-Router/dp/B00008SCFL/ref=sr_1_3?ie=UTF8&qid=1324423122&sr=8-3