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As far as I know, the felt paper would serve as a moisture barrier to prevent moisture from seeping up through the concrete and allowing your flooring to mildew from underneath. The moisture might be seeping even on an apparently dry concrete floor and just evaporating unnoticeably when it is not covered. Some experts advise testing your concrete for moisture by taping a 2 x 2 foot piece of plastic sheeting to the floor and letting it sit for three days. If water beads underneath it, you have moisture seeping up and need a moisture barrier.
My thoughts are: why bother testing? A moisture barrier of a 6 mil piece of sheeting costs less than $20, and it does no apparent harm, and will protect the flooring from future moisture problems that have not yet developed. The only issue is how you will secure the sleepers to the floor, which is resolved by placing glue compound both over and under the plastic where you would place the sleepers. The plastic gets sandwiched between two layers of glue, and the sleepers are secure.
Again, a moisture barrier is not necessary if you do not have moisture, although it will be a better job if you include it. Builders' felt is not as good a moisture barrier as plastic, but it is a commonly used material.
As for the best way to fix the sleepers to the floor, I have read that troweling down a glueing compound is sufficient. You can also use concrete nails/screws, but make sure they end up flush with the top of the sleepers.
[This message has been edited by Lawrence (edited December 12, 2000).]