Just a note: Wireless Internet and Wireless Network are two different things.
Real Wireless Internet would mean you don't even have a some type of cable coming into your hose for internet connection, so no ADSL or Cable, but maybe some kind of satellite service or city-wide wireless WAN or something.
What i think Vince is looking for (and the replies so far describe) is just a wireless local network. You will still have your normal wired internet connection, but connected to that you have an accesspoint from where your machines can connect wirelessly. Or alternatively you could buy a wireless router, which is an accesspoint and modem/router in one. Since you already own a modem/router I'd go for just a simple accesspoint, which you can connect to the modem/router's ethernet port. Something like this should do just fine:
http://www.linksys.com/servlet/Satellite?c=L_Prod...&lid=5260733028B07 (but make sure to doublecheck before you buy, I don't haven't checked your current modem's specs)
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