I am goin gto re-do our bathroom and will be tearing off all the sheet rock.  I would like top insulate the walls (interior) that face a bedroom and the kitchen for sound proofing(dont ask...)  should I use a vapor barrier type insulation or plastic under the rock to keep the moisture out of the insulation or being that it is a interior wall, I dont have to worry about this.  I just want to make sure it does not start to grow mold and stuff.

thanks.

First of all, two layers of drywall (each side) will give you way more sound proofing than any insulation will.  The seams should alternate, never lining up with each other.
Second, any little penetration in the wall will leak sound.  Make sure that any electrical boxes, medicine cabinets, etc. are in their own "bay" of the framing.  By "bay" I mean the space between two studs.  There should only be one penetration, and on only one side, between any two studs.
Are you doing tile over the drywall?  I would look into dens-shield or dens-glass no matter what.  This stuff is made to withstand moisture like no other.  Check with a drywall supply house (not Home Depot or Lowes) and they should be able to tell you which one would be better for your application.  Either way this stuff kicks the shit out of green board.