I would recomend using TREATED 2x2 or 2x4's laid on their sides if you have enough clearence for doors etc. I would screw them down to the concrete using masonary screws (tapcon). I would definatly reccomend instaling a vapor barrier to keep your floor form rotting. You shoulden't have to put down a subfloor due to the thickness of your flooring. Also if you live in a colder climate it would be wise to stuff some 1 1/2" rigid foam insulation between your nailing strips to keep the cold out.