Using VSTO 2005 and Office 2003 you can create an Action Pane (see video) . This is a document level object, which mens that it is attached and visible only when the document is open. Now in using VSTO 2005 SE and Office 2007 you can create CustomTaskPanes...

One of the most common questions I get is what are the differences between VSTO 2005 and VSTO 2005 SE . This can be a little confusing because of the way that the 2 products overlap and the fact that there are 2 versions of Office (2003 and 2007) involved...