FYI: Want to build VSTO AddIns for Office 2007? VSTO 2005 SE Download Available Now!
VSTO 2005 SE is a free download for Visual Studio 2005 Tools for Office AND Visual Studio 2005 Professional that will allow you to build VSTO AddIns for Office 2007 applications.
Note if you installed the CTP this summer...
"VSTO “v3” CTP users: If you previously installed any of the VSTO “v3” CTPs, you need to completely remove the CTP software from your computer before you install VSTO 2005 SE. Because the CTP’s ability to uninstall itself is very limited and unreliable, we strongly recommend that you restore your system in its entirety from a backup made before any VSTO “v3” CTP software was installed. This will require you to reinstall Visual Studio as well. If VSTO 2005 SE is installed on computers where VSTO “v3” CTP software is installed, or was installed but not removed properly, you may experience various error messages and failures. (If restoring a backup of your computer is not an option, you can try to uninstall Visual Studio 2005 and all related products from your computer, and then install them again. This is not guaranteed to completely remove the CTPs, but it has been reported to be sufficient to enable VSTO 2005 SE to work.) "