Question: how do i get the width and height of the entire screen in XNA?

Answer: 
Empirically I've found that in XNA 4.0 I need to use 

```
GraphicsDevice.Viewport.Width
GraphicsDevice.Viewport.Height

```

when running windowed mode, as I find

```
GraphicsDevice.DisplayMode.Width
GraphicsDevice.DisplayMode.Height 

```

gives me the resolution of the entire screen.

Hopefully this helps someone else out.
GraphicsDevice.Viewport.Bounds - this returns Rectangle2D and it has parameters Width and Height.