KD Hallman, the General Manager for the Visual Studio Tools for Office team, just announced “Cypress”. Cypress is a free update to VSTO that adds support for Office 2007 development and it will ship when Office 2007 ships this year. It is an add-on that will install right on top of your existing Visual Studio 2005 installation and give you new projects to target Office 2007.
You can find more details about Cypress in KD's MSDN Forum posting at http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=459132&SiteID=1
Or see KD and myself talk about Cypress on Channel 9 at: http://channel9.msdn.com/Showpost.aspx?postid=201396
You can get a CTP of Cypress at http://msdn.microsoft.com/vstudio/future/ and view some demos of the CTP at http://channel9.msdn.com/Shows/In_the_Office