I haven't made any nice mod package or anything, but I did a test implementation of TinyMCE for PunBB a while ago, and thought I should share it with you.
You can visit the forum at
If you go to "Post Reply" you can see a link to the right of "Smilies: on", where you can toggle TinyMCE on and off, and it converts between BBCode and HTML.
In the "viewtopic.php" page (if you use quickreply) there is no backend modifications, just added the scripts and replaced the "process_form(the_form)" with my own wrapper function "submitForm(the_form)".
On the "post.php" page however, there are some modifications to the source file, you need replace the "process_form(the_form)" that is "echoed" by PHP (ugh, sorry but thats ugly coding guys, USE TEMPLATE SYSTEM!).
On edit page, no changes to PHP source was neccesary.
Edit: Btw, please note that there is a known bug in Mozilla/Firefox that for some reason when WYSIWYG editors are used, meta-refresh doesn't work, so your users will have to click the link after they posted to be redirected. Dont blame us, blame Mozilla/Firefox dev team