Yesterday we released the Visual Studio Tools for Office 2005 Second Edition (VSTO 2005 SE) Beta. This version of VSTO is a free download that you add to Visual Studio 2005 Pro or VSTO 2005. VSTO SE enables Office 2007 add-in development and it also enables Office 2003 add-in development for the big 6 Office apps: Word, Excel, Outlook, PowerPoint, Visio and InfoPath. InfoPath even has designtime support like Word and Excel in full version of VSTO 2005.
Read the full announcement here: Announcement