Subfloor or not?
Most floor manufacturers will not warrant any type floor installed below grade...so it matters not what type of wood floor you install in a basement....It will be void of warranty...so don't do it.
Floating the floor on the concrete will make it hard like concrete: uncomfortable and unforgiving. However, it will run fewer risks of rotting out, breaking, slumping, or what have you. On the other hand, building a subfloor makes the room more comfortable, subtly absorbing sound, vibration and footsteps. However, that comfort also comes with the price of adding installation costs and the potential of slumping, rotting, and the like, especially if it floods.
That said, I would install a subfloor if you plan to use the room at all.
[This message has been edited by TchrMommy (edited December 13, 2003).]