I have been read this article about Notes 8 sidebar and toolbar thanks to my boss that sent me the link.
The most interesting things I have found, for me, are IViewPart, that is the object I was looking for when I was trying to develop the Rss, and that compounds the base of this kind of visual plug-ins.
I have had problems to develop a plug in till I found this object.
In addition, the explanation of how extension points are deployed in Lotus Notes client. It brings me near of some concepts I have read about Composite applications.
I need to read more about composite applications!!