Blend 3(wpf ) project in Visual studio 2008

Question

I have a project that created by expression blend 3 (wpf) and wanna add this projetc to a 
C# win_app_form project (my strat up project ),but when I give an instance of it (wpf project ) ,error occurs.
what should I do ? in generally can we use a wpf(blend 3) project in visual studio as a reference?!
In my win form I have a button for example like this 

private void button1_Click(object sender, EventArgs e)
        {
            wpfapp.App wpfinstance = new wpfapp.App(); //is it true?
             wpfinstance.     //what should i write here , it has only InitializeComponent property that gives error .

        }
how can I instance new wpf_window in my win_form(visual studio) and show it??!
The only way is creating usercontrol(as .dll)???
is there any way to run my wpf app by pressing a win form button???