Visual Studio Tools for Office (VSTO) is a bit of a funny creature. It needs to adapt with each release of Office, and also with each release of Visual Studio. The next version is code named Cypress and it works with either Visual Studio 2005 or with Orcas, and with Office 2007. Charles Sterling blogged the announcement just before TechEd:

Cypress will include the following functionality and release at about the same time as Office 2007:

·    Application-level add-ins for the most popular Office applications including Outlook, Excel, Word, PowerPoint, InfoPath and Visio.  This is currently the #1 most requested feature for VSTO – safe loading, unloading, and management of managed add-ins.  I’m thrilled that we’re going to be able to provide this functionality to developers much earlier than anticipated.

·    Office key feature support: programming model and runtime support for Ribbon, Custom Task Panes, and Outlook forms regions.  Office’s new UI contains exciting extensibility opportunities and Cypress will enable VSTO’s simple coding experiences like IntelliSense. 

·   Maintainability and compatibility are core principles for the VSTO team and Cypress will also ensure that your applications built on Office 2003 with VSTO 2005 continue to run with Office 2007. 

Cypress is an add-on and is incremental.  It is not, itself a complete Visual Studio product release.  Anyone who has a licensed version of Visual Studio 2005 will be eligible to download Cypress for free.  However, I want to be clear that Cypress is not a super-set of all the VSTO 2005 functionality that was made available for Office 2003 replicated for Office 2007.  As promised, Excel Workbook and Word Document project support for Office 2007 will come on-line in VSTO “Orcas”, and be made available in upcoming “Orcas” CTPs.   Also look for the exciting new VSTO “Orcas” functionality, such as the visual designers for the Ribbon and Custom Task Panes, and Outlook in these “Orcas” CTPs.

There's a Channel 9 video in which KD Hallman and Eric Carter discuss features and goals of Cypress and beyond that's a pretty good starting point.

If you can stand the endless rounds of public betas, CTPs, and trying to work out which versions need each other or conflict with each other, you can have a lot of fun this summer!