Yes, you can. Buying a wireless network adapter would be the easiest way to do so, yes. Be sure that the chipset your adapter uses has Linux drivers. If it doesn't, it can often be made to work, but it's easier to just plan ahead a little.http://www.linux-drivers.org/http://linux-wireless.org/Wireless/Drivers/
Good places to start, and a Google search will yield much more information. There was another popular website, but I can't for the life of me remember what it was.