help required in downloading files from a folder!!!!

 I have a web page with a listbox which display the contents of a folder...this folder has pdfs and rar files..it actually consists of ebooks and study material...i tried following code.i was successful in finding the full filename and filepath...what next is to be done????
Code:
 Dim filepath, st, filename As String
        st = ListBox1.SelectedItem.Value()
      
        filepath = Server.MapPath("~\StudyMaterial" + st)
        filename = Path.GetFileName(filepath)
        Response.Clear()
        Response.ContentType = "application/octet-stream"
        Response.AddHeader("Content-Disposition", "attachment; filename=" + filename)
   ...