Do a google search for 'php twitter' and you will find some info including on the twitter api. This seems inline with what you are wanting to do.
http://www.webmaster-source.com/2009/04/05/post-to-twitter-from-a-php-script/Just remember you will want to sanitize the output, and to post to individual accounts per forum would require a bit more work retrieving the forum number and a switch statement.
Good luck!
