I am using Addin Express to do this , and below are the steps I have followed
1) Add a AdxRibbonTab and ImageList in the Visual Designer.
2) In the Imagelist one can add several images , and access them by the index, 0 being the first image in the Imagelist.
3) Add the buttons in the Ribbon tab, in my case I have added two Convert to PDF, and About.
Now you can tie up the button events and write your code there.
Now I have created an installer for this addin and below is the snapshot taken from Outlook 2007.
I am not sure of the the numbers which are showing, buts when I am taking a screenshot and pasting it to Paint, they are appearing. If anyone knows the mystery please let me know