Posting from an outside form

Hello all,

I am trying to integrate PunBB into my site, and I want to allow guest users to post their message from a form on the website homepage (which is outside the PunBB installation, but on the same domain name).

How should I go about generating this form, or rather, the script that would add a post to the forum? Is there a direct way or do I need to write a script?

I was looking at both post.php and common.php and couldn't find a function that would simplify this task.

Thank you all and I apologize if this was answered previously. I would be grateful for documentation hints as well!