How do I develop addin for MS Outlook that works with all
1. Outlook 2010
2. Outlook 2007
3. Outlook 2003
I have developed addin that works well with 2010 and 2007 BUT NOT with 2003.
I want something like this that works well with all the above three 🙂

You need
VSTO(Visual Studio Tools for Office). Here is an article to get you started.You can also check out
Office Development Center.