[Jawelin]

Oh, YES it is !!!
I added in showthread.php something like:

PHP Code:

    if (trim($forum[title])=="ANNOUNCEMENTS") {
      $threadtitle=urlencode("Announcement #$threadid Reply: '".$thread[title]."'");
      eval("\$replyopenclosed = \"".gettemplate("showthread_replynewforum")."\";");
    } 


and created a new template showthread_replynewforum :

<a href="newthread.php?s=$session[sessionhash]&forumid=XX&subject=$threadtitle">
<img src="{ replyimage }" border="0" alt="Post a Reply to This Thread in Another Forum!"></a>

with 'XX' as my chit-chat forumid...
GREAT !!

Thanks for your support.

Next step: to look for an existing thread with such title instead of creating a new one each time ...