Please have a look at Maxime Bombardier’s Blog on MSDN Blogs for his article on Visio Stencils for SharePoint 2007. You can download them directly from his blog and is a great addition if you are busy documenting SharePoint sites and structures. His stencil is for SharePoint objects such as sites, document libraries, site collections, surveys, etc. Maxime also has a link in his article for a stencil that with SharePoint Servers for documenting SharePoint architectures. This stencil can be found on the Blog of Mart Muller here
For your convenience I have downloaded the files to my blogsite here:
Of Course check the blogs of Maxime and Mart for updates [:D]
Hi Dirk, There are some exceptional Visio 2007 stencils for SharePoint 2007 Design and Architecture, not free, but well supported and with over 1000 shapes. Check out http://www.visio-for-sharepoint.com