Required download for anybody doing something with VSTO 2003 & 2005: Microsoft IntelliSense XML Files for Microsoft Visual Studio Tools for the Microsoft Office System Solution Developers
Adds summary descriptions of types, members, and parameters to IntelliSense ToolTips in code and in the Object Browser for Microsoft Office Word, Microsoft Office Excel, Microsoft Office Outlook, and Microsoft Office Shared PIAs in Microsoft Visual Studio .NET 2003 and Visual Studio 2005.
[Tx David and Christophe for the pointer]