The subject of MediaWiki integration has come up before (e.g. http://wordpress.org/support/topic/132820?replies=14), and a partial solution created, but I decided to take a different approach and integrate directly with the WP core instead of peeking into the database. This allows a more seamless integration.
Currently it's very much at the alpha stage, but it's up and running - take a look here if you're interested: http://ciarang.com/posts/mediawiki-with-wordpress