Using Drupal and Plone together

I'm new to the forum so please forgive me if I'm posting this in the wrong place. We have an extranet site for our customers built in Plone that has a great deal of functionality and documentation, but the look and feel and the community features are lacking, so we're looking at Drupal. We've already built two of our external sites in Drupal 5.6, including a number of custom-built community features, and we'd like to re-purpose some of that functionality in the Plone-based extranet. Because there is so much functionality and documentation in the Plone-based site, we're wary of trying to redo the whole site in Drupal, but we would like to add a few Drupal areas and have them still work well with the Plone-based based areas.

So the gist of the issue is how Plone and Drupal pages can work together in terms of passing usernames/permissions, etc, as well as sharing a common look and feel. Is there any documentation or advice on this? Thanks for any help on this front. I find a lot of comparisons between Plone and Drupal online, but haven't found anything about the two working together yet.