If you don't want to loose ceiling height, you will need to remove the celing covering to gain access to the floor joist cavities.
A product we've had great sucess with is Roxul (http://www.roxul.com ... read more
In a word...yes.
As Katie mentioned, you need an appropriate length fastener and a cap nail is ideal.
What you haven't mentioned is what the wall depth is as well as climate. If you have 2x6 walls, 1 ... read more