All you do in the moment is to create a new document in the backend and fill it with values. It is like creating a word document without opening it...
You need some more code to actually SHOW the document you created. In addition you need to assign a Form, otherwise Notes will not know, how to display this document:
Dim session = AutomationFactory.CreateObject("Notes.NotesSession")
Dim notesdb = outlook.GetDatabase("", "")
Dim ws = AutomationFactory.CreateObject("Notes.NotesUIWorkspace")
notesdb.OpenMail()
Dim doc = notesdb.CreateDocument()
Dim msg = "Hey whats up"
doc.ReplaceItemValue("Form", "Memo")
doc.ReplaceItemValue("SendTo", "person@temp.com")
doc.ReplaceItemValue("Subject", "Hello")
Dim rtitem = doc.CreateRichTextItem("Body")
rtitem.AppendText(msg)
ws.EditDocument( True, doc )
As I do not use silverlight I unfortunately could not test the code, but It should point into the right direction.