Yes. Either a card or a USB device.

Seems like a wired connection would work just as well (if not better) than a wireless one.  But maybe I'm not understanding the OP's question.

I have an existing wireless network that I'm wanting to add the new desktop. The only wired slot available is taken up by the router. Having said that, I see there are more slots available on the router. I assume I could plug in a cable to one of those slots and run it to the new computer in lieu of a card?

Okay. Thanks for the verification.

Having said that, I see there are more slots available on the router. I assume I could plug in a cable to one of those slots and run it to the new computer in lieu of a card?

That will work fine.  Connecting the new desktop to the router by ethernet cable (just as with your other desktop) is the preferred solution (it's more reliable, faster, and you won't need to buy a wireless card).  The negative is that cabling is often not-practical (for instance, if the desktop will be in another room or on another floor).

Good to know. I have about a 10 foot ethernet cable on hand.

Thanks for the assistance.