Here you go:
$this->ipsclass->DB->table_exists => $this->DB->checkForTable( $table );
$this->ipsclass->DB->field_exists => $this->DB->checkForField( $field, $table );
API instead are not needed anymore, if you want to create a topic you have to include directly classPost:
require_once( IPSLib::getAppDir('forums') . '/sources/classes/post/classPost.php' );
$this->classPost = new classPost( $this->registry );
I can give you the code to create a new topic, but you won't understand exactly how it works having an encoded file.. better to wait for the unencoded version in my opinion :)