WordPress hook before inserting post into database

I need to do check the inserted post for certain keywords and perform some functions depending on the keywords found.

is there a wordpress hook that executes “just before the post is inserted into the database” ? Or will i have to modify wordpress core ?

Also, i will need to prevent the post from being inserted into the database if some keywords are found. is this something that can be done with a hook ? Or will a core modification be needed ?

Available actions:

1. pre_post_update – Runs just before a post or page is updated.
2. publish_post – Runs when a post is published, or if it is edited and its status is “published”.
3. save_post – Runs whenever a post or page is created or updated, which could be from an import, post/page edit form, xmlrpc, or post by email.
4. wp_insert_post – Same as save_post, runs immediately afterwards.

More info: Plugin API/Action Reference

Usage:

<?php
add_action('action_name', 'callback_name');