Do I need special equipment in order to connect two computers to the
internet when there is a 4 inch concrete pad between floors and one computer is upstairs and the other downstairs.  We have vents in the ceiling down and floors up, as well as a stair well.  Will placement be a problem for the wireless equipment?

   You can get a wireless router and see if it works wirelessly.  If not, you can always run a cable from the computer that cannot hook up wirelessly and plug it into the back of the wireless router.