Well, you're asking a few different questions there. I'll start by answering your main question which is about how to display a debug representation of a `BoundingBox` object.

**How to render a BoundingBox**

The easiest way I can think of is to get the corners of the bounding box and render it using a line list primitive. You can get the corners of the bounding box using the `BoundingBox.GetCorners()` method ([documentation](http://msdn.microsoft.com/en-us/library/bb197066.aspx)). This method returns 8 positions in world space. The first four represent the front face of the bounding box, and the final four represent the back face of the bounding box. 

Then simply create a `VertexPositionColor` vertex for each of the corners, and render lines between them in the correct order. Whether you use indices or not is up to you.

No need to implement it though, just **[download this sample](http://create.msdn.com/en-US/education/catalog/sample/shape_rendering)** from the education catalog, add the `DebugShapeRenderer` class to your project, `Initialize` it and finally use the provided `AddBoundingBox` method. It does pretty much what I described above.