Congratulations on the quick action on creating this module. It will be interesting to see it evolve.

You may want to look into the RDF API currently being developed for Drupal 6.x. While still at an early alpha stage, it provides comprehensive RDF functionality (including RDF parsing which you will need to handle Calais responses) and integration with the ARC2 library.

You can see screenshots of the administration facilities provided by the module at http://flickr.com/photos/bendiken/sets/72157603487819775/detail/ and documentation is currently being put together at http://drupal.org/node/219852

Just to give you an example, fetching and parsing an RDF/XML file from a URL is more or less painless with the RDF API:

$data = rdf_unserialize(file_get_contents($url), array('format' => 'rdf+xml'));

Building on top of the RDF API also means that the metadata you retrieve from Calais will automatically be made available to other Drupal modules plugged into the API, including, for example, rich data visualization browsers such as Exhibit.

In case you are interested in collaborating, feel free to contact me with any questions you may have.