Check out Andrew’s VSTO presentation he did @ the ACT user group with Athena:

http://msevents-as.microsoft.com/CUI/WebCastEventDetails.aspx?EventID=120465474&EventCategory=3&culture=en-AU&CountryCode=AU

Visual Studio Tools for Office

Microsoft Visual Studio Tools for the Microsoft Office System is a new technology that brings the power and productivity of Visual Studio .NET and the .NET Framework to business solutions built on Microsoft Word 2003 and Microsoft Excel 2003 and beyond.