If you are developing addins for Office 2003 and you are in Vista this may be for you.

Quote

This update fixes an issue in add-in development for Microsoft Office 2003 using VSTO 2005 SE on Windows Vista.

During the development of Windows Vista, several key investments were made to vastly improve overall quality, security, and reliability from previous versions of Windows. While we have made tremendous investments in Windows Vista to ensure backward compatibility, some of the system enhancements, such as User Account Control, make Windows Vista behave differently from previous versions of Windows. These investments affect Visual Studio 2005 Tools for Office Second Edition.

This update does not install a full version of Visual Studio 2005 Tools for Office Second Edition.
 
Download it here and install it over your existing SE installation.