How to write add-in for SharePoint Designer 2010

I'm looking for information on writing an add-in for SharePoint Designer 2010. If you go to File->options there is a possibility to add COM add-in's, I would like to write one, preferably using C#.

Any pointers to documentation/examples? What SharePoint specific classes are accessi开发者_如何学运维ble?

http://vsto.codeplex.com/releases/view/17375 -- This might be helpful to you.

http://www.deque.com/products/deque-labs/sharepoint-designer-2010-add-in --This is the way you can install any adding.

There's some information that may be useful on this forum: http://social.technet.microsoft.com/Forums/en/sharepoint2010customization/thread/be3c20bf-f842-46ae-8cf1-a2dd81a6c4dc

I haven't tried it myself though.