Help-Wireless Networking w/Dimension 4500S

Hello,

 

I need help setting up my wireless netwok.  I have cable broadband.  The main computer near the cable modem & wireless router I plan to buy is a Dell Dimension 4500S desktop.  We have 2 other computers: a mac & a pc both with integrated wireless cards.  I checked to see if the desktop had a network adapter and it listed the modem and 1394 network adapter.

 

Is this what I need?  If not what do I need to hook the desktop to the wireless router?  Can I get something external?

 

Thanks for your help!