I was just diagramming an Exchange 2007 deployment and came across the Microsoft Office Visio Stencil Containing Shapes for Microsoft Exchange Server 2007, a free download from Microsoft.
This stencil and template provided enable you to create Visio drawings that contain Exchange Server 2007 objects. These shapes include icons for Exchange 2007 server roles, networking, telephony and Unified Messaging objects, Active Directory and directory service objects, client computers and devices, and other Exchange organization elements.
To use this stencil, place these 2 files (MicrosoftExchangeServer2007_Icons.vst and MicrosoftExchangeServer2007_Icons.vss) in your local C:\Documents and Settings\yourname\My Documents\My Shapes folder.
In Visio, click File, click Open, and then go to your My Shapes folder. Open the MicrosoftExchangeServer2007_Icons.vst file. The shapes will appear in the Microsoft Exchange Server 2007 stencil in the Shapes pane.
This download requires Microsoft Office Visio 2003 or later.