From Add-in Express:
Use visual designers of Add-in Express 2007 for .NET to develop secure and isolated, version-neutral and feature-rich, deployable and updatable extensions for all available Microsoft Office versions, including Office 2007, 2003, 2002 (XP) and Office 2000.
Project templates of Add-in Express support all Office extensibility technologies including COM add-ins, smart tags, real-time data servers and Excel user-defined functions.
With Add-in Express 2007 you can create both application-specific extensions, e.g. Outlook plug-ins or Word smart tags, and shared extensions that work on all end-user applications from the Microsoft Office family: Outlook, Excel, Word, PowerPoint, Visio, Project, MapPoint, Publisher, Access, FrontPage and InfoPath.
Use visual designers provided by Add-in Express to:
Build new or customize existing toolbars, menus and sub-menus on Microsoft Office 2000 - 2003.
Add new or customizing existing tabs for the Office 2007 Ribbon UI, build the Quick Access Toolbar and the Office Menu.
Develop your own task panes for Office 2007 applications.
Access any Office objects, handle any Office events.
Customize Microsoft Outlook windows, views and forms with advanced form regions.
Develop application-level keyboard shortcuts.
Add Outlook option and property pages.
Use any .NET controls on Microsoft Office toolbars.
Intercept any built-in controls.
Develop Smart Tag recognizers.
Program Microsoft Excel RTD servers and topics.
And, write a version-neutral applied code that works transparently on all Office versions.
Add-in Express 2007 for .NET is developed in C# and directly supports C#, Visual Basic .NET (VB.NET), C++, J# and Delphi for .NET. Add-in Express supports Visual Studio 2003 and 2005, .NET Framework 1.0 and higher.