The easy answer would be for you to implement a very basic tool to help to position your objects in your scene. Most game engine will have an editor for you to do so but since XNA is just a framework, you could implement a very simple system with your keyboard and arrow to move your text around and output on screen the X and Y position. It's not perfect but it should save you some time.
Also:
Vector2 mousePosition = new Vector2(Mouse.GetState().X,Mouse.GetState().Y);
Console.WriteLine("My Cursor is at: " + mousePosition);
Don't forget the IsMouseVisible member of Game to be able to actually see your mouse cursor.
Hope it helps!