Bruce take a look in
http://jaggedplanet.com/imerge.html to mosaic program. The best and easiest. Short, light, don't need installation. You have full control of position and amount of images. It is like to play with them.
The problem of mosaic is capture all field, with many photos, with clear sequence to don't be confused when assembling. And mainly, get an equal or similar graphic process of all images to have a smoth transition between them. As I wrote:
Be patient ! 