Here’s a good article on how to customize the Outlook 2007 Command Bar:
Just one problem: It doesn’t work. Or doesn’t seem to. The author forgot to mention a key detail. If you don’t actually see the menu after you build and debug-run the project, it doesn’t mean it isn’t there. Try going to the command bar. Pick the View menu, then Toolbars. Once you pick the Toolbars option you should see a MyToolBarButton. That’s your baby. Pick that selection and you should see “My ToolBar Button” command button show up on the command bar.