You need a wireless router.  One with 802.11g capabilities should be adequate, as the higher speed models will not work at the higher speed unless both the router and the wireless network card are from the same manufacturer.   Furthermore, the 54 Mpbs speed of 802.11g routers is still faster than the fastest broadband internet connection, so any higher speed is only useful if you frequently transfer large files between computers on the local network.  Security issues can be easily solved by enabling the security features of the router.  See the following:

http://www.microsoft.com/windowsxp/using/networking/learnmore/bowman_05february10.mspx

http://www.ezlan.net/Wireless_Security.html

http://www.pcmag.com/article2/0,4149,1277020,00.asp

Steve

Thanks for your help! All 3 articles were very informative albeit only a little confusing because of some of the jargon. But that's okay...so long as I follow the instructions, it should work out fine!

Chris