Microsoft has released the Visual Studio Tools for Office 2007 bits . These are also know as VSTO 2005 SE (Visual Studio Tools for Office Second Edition). In addition to all the new Office 2007 applications (Word, Excel, InfoPath, Outlook, PowerPoint, and Visio), these also support Office 2003 applications (Word, Excel, Outlook, PowerPoint and Visio).

You can get more information on MSDN.