Wige, knowing Joomla urls as I do, I think he'll have to do one to one redirects, since there won't be exact hierarchy matching.
Anyway, dux, if you include sitemaps in the various search engine formats, this will also help in getting things sorted out.
You might want to look at drupal as an alternative to joomla. There is a way in drupal to specify exactly which url will show for which piece of content, so you can avoid all those redirects, and continue your hierarchy/url structure the way it is now.
Path: readable URLs | drupal.org