Notes Integration from any third party application is not an easy straight forward thing. However Interop.Domino.dll provided by IBM Domino helps do all basic operations on a Lotus Notes Database.

When it comes to using BizTalk to integrate with Lotus Domino, there is no LOB Adaptors available with BizTalk. Not even 2006R2. Well, there is no even a third party BizTalk Adaptor for this purpose.
There are few providers for universal adaptors for Notes but, it takes the same effort as using Interop.Domino.dll and code out your interface.

Following link will help you get a detailed SDK typed details on each classes and its usage from the Interop assembly for Notes.
https://sametime.aspeninstitute.it/help/help65_designer.nsf/Main?OpenFrameSet&Frame=Topic&Src=%2Fhelp%2Fhelp65_designer.nsf%2FContentsIntro%3FOpenPage%26AutoFramed

Here is an example on how such a simple interface may look:

NotesSession nSession = new NotesSession();
NotesDatabase nDB;
NotesDocument nDoc;
nSession.Initialize("mypassword");
nDB = nSession.GetDatabase(@"ServerName", @"DatabasefileName", false);
if (nDB == null) throw new Exception("Notes Database not available");
if (!nDB.IsOpen) nDB.Open();

nDoc = nDB.CreateDocument();
nDoc.AppendItemValue("ItemNo", "00001");
nDoc.AppendItemValue("ItemName", "Rubber");
if (!nDoc.Save(true, false, false)) throw new Exception(@"Failed to save");