Metro a.k.a XPS & 3D graphics-Collection of common programming errors

Hi
I have a few qeutions to ask :
#1: 

I was busy with Avalon working trough the SDK documentation and examples and decided to create a bit of 3d graphics, but when I tried to create a tag in my tag  is gave me an error saying that the tag was an invalid child element, although when I build the application is still runs. Why is it doing that? Is it supposed to do that?#2:I am also interested in working with the new XPS specification but, I am having trouble creating such a project. What I want to ask is the System.Window.XPS.Packaging API available in this build as well as, I saw I video about metro where he used a new printing driver (I think it was the Microsoft digital document driver really not sure!!!) to print the XPS document to an file are these drivers available somewhere or are they only going to be launched with Indigo?

How do I go about creating a ReachPackage document project?