Blue Peter strikes again!
Never knowingly understood.
Hidden, and screw into the mesh side (they will sink in). Or you can
use small screws if you want. The nails should be rink shank, so they
don't pull out. Also, put something soft (e.g. an old sheet or
newspaper) between the floorboards and the hardboard or you will get
squeaks. If you lay it damp, it will tighten up and you will avoid
I'd recommend a small electric nail gun. Much quicker than doing by hand
... but less environmentally friendly... :-)