Adding a forum post as part of a larger script elsewhere on website...

I'm setting up one of the final features of my site, and have one little request for assistance with this problem.

How easy/hard/possible would it be to do the punBB part of the following script:

? someone navigates to page
? they enter data about a 'project' (title, description, etc)
? information is added to one database table (title, date started, user id, etc etc)
? [punbb part] title, description, userid, date posted, etc are used to create a new subforum and first thread in that subforum.

i don't have the subforum mod installed yet (it's on the list).

i have decent enough php/mysql knowledge, but i'm having trouble understanding "post.php".

how would i go about, let's say, just having the content of a file called http://site.net/create/project/index.php, containing "subject" and "message" fields, and a submit button, where "subject" is used for both the subforum and the thread title.

what would the code be?

thanks muchly