bbPress.org

Untested. Actually the forum is deleting some of the code so use it from here:

http://pastebin.com/f54a958de

<?php

/*

Plugin Name: Wiki Link

*/

add_action('post_text','wiki_link',200);

function wiki_link($text) {

$url="http://example.com/path_to_wiki?terms=";

$text=preg_replace("/([[(.+?)]])/si","<a class='wiki_link' href='$url$2'>$2</a>",$text);

return $text;

}

?>

the above is missing two $2, should look like

<a class='wiki_link' href='$url$2'>$2</a>