Is your desktop near the router? If so, simply purcahse a regular old PCI Ethernet card (less than $30) and an appropriate length ethernet cable ($< $10) and you'll be all set!

I have an ethernet cable that came with the router. I just need someplace on the computer to plug it into....Thank-you for your help

make sure you have a free PCI slot before you do that (some tiny form factor desktops might not) ... and check adds at stores like staples, best buy, compusa, office depot, and office max ...  every couple of months there will be free ethernet cards

if you got a broadband modem with your broadband service, they normally include a PCI ethernet card.  You just need to install in on your desktop.  which desktop do you have.  if you ask, then people can tell you if you have a slot available.