title: C# dual Outlook 2007/2010 VSTO Add-in
body: <p>We need to create a VSTO add-in in C# that supports both Outlook 2007 and 2010.</p>
  
  <p>To start off we created 3 projects:</p>
  
  <ol>
  <li>File->New Project->Office->2007->Outlook 2007 Add-in</li>
  <li>File->New Project->Office->2010->Outlook 2010 Add-in</li>
  <li>File->New Project->Windows->Class library</li>
  </ol>
  
  <p>All shared code is in project #3.</p>
  
  <p>So far, we have partially developed the add-in and have been using ClickOnce deployments for testing.</p>
  
  <p>One day, we noticed someone installed the 2010 add-in for 2007 Outlook and had no ill effects whatsoever.</p>
  
  <p>So a few questions:</p>
  
  <ul>
  <li>Is there any reason to create the
  2007 VSTO project?  Can we just
  create the 2010 project?</li>
  <li>Or is the only difference the version of
  the office runtime that is
  bootstrapped by the ClickOnce
  installer?  Can you just install the 2010 runtime for Outlook 2007?</li>
  <li>If there is no difference, why are
  there two Visual Studio project
  templates?</li>
  </ul>
  
  <p>In our final solution, we will be using a WiX installer, which is also working thus far.  The WiX installer will be simplified greatly if we can use 1 project for the add-in.</p>