Insulation, Radiant and Vapor Barriers - vapor barrier

I have been told that the drywall is sufficient for a vapor barrier, is this true? I am remodeling my kitchen, and am at the insulation stage. I have one outside wall, and one wall to a three season room that is unheated. there is also a crawl space above the kitchen about four feet wide, from outside wall. if the drywall is not suff. how could I add a vapor barrier to the upstairs( for that crawl space) and how should I insulate the rest?
thanks

http://www.eren.doe.gov/consumerinfo/refbriefs/bd4.html This is an U. S. Dept. of Energy brief on Vapor Diffuser Retarders (VDR) or vapor barriers if you prefer.

Sheet rock does not qualify as a vapor barrier, some paints and wall paper may.

Insulation is applied between conditioned and unconditioned spaces. The 3 season room, crawl space and if the ceiling in the kitchen is below an attic, they are considered unconditioned spaces. This is also referred to as the thermal boundary. If you read the brief they talk about the air boundary. The air boundary prohibits air from entering the insulation. So in most cases the vapor barrier is an air boundary.

Insulation in crawl spaces are usually held up with joist hangers with the vapor barrier touching the floor of the kitchen. Go to any home improvement store and ask for them and they'll show you it and how they are installed.