Does the 1100 desk top require a wireless card?

I got a Belkin N150 wireless router to be used with my dell 1100 desk top. Half way thru the Belkin on screen set up directions, it says to locate and turn on the wireless antenna switch. I followed the "How to find the wireless antenna on and off switch" link from the help center, found it could be a switch on the computer, a key, or a combo of keys. Followed link to owner's manual and found nothing about a wireless antenna. Several searches in the manual's search box brought up nothing, not even using word search with "antenna" and then "wireless". Despite having followed a wireless antenna link that listed 1100 desk top among models with more info on wireless antennas, does in fact my 1100 desk top does not have an on/off switch, because it has no wireless antenna? Am I just missing something? Do I need a wireless card? I read post about internal modems, is that just for lap tops? If not, I am using an external modem and the router is hooked up to that.