Here was my original post of a few days ago:
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I need to lay a plywood sub-floor (ready for engineered hardwood to go on
top) over a concrete floor in my first floor family room. What is the best
way to fix it to concrete? I have never done anything like this before, but
I understand there are nails that will drive themselves down into
concrete....is that right? Are they easy to use?

Would this method be better than some kind of thinset/mortar etc?
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UPDATE
Some kind souls on the group gave me some ideas about nailing/gluing plywood
onto concrete or using sleepers. Well, I went to Menards today and they
showed me some purpose made 2' square boards cut with tongue and groove,
with a plastic base. The base has small feet which keep the wood approx
1/8 off the concrete.

This seems to be the perfect solution. Easy to install (it just sits on top
apparently, though I might glue a small number on to give it some added
rigidity) with tongue and groove and no glue required, plus the base gives
you protection from damp.

Anyone else tried this? I am pleased so far (taken me an hour to do around
1/3 of a 12x18 room). It is more expensive than plywood, but, according to
my back-of-a-napkin calculations in-store, only about 20% more. And I got
it all in the Jeep!

Mat