<?php
$insert_sql = "INSERT INTO users (first_name, last_name, email, bio, facebook_url, twitter_handle) " .
"VALUES ('{$first_name}', '{$last_name}', '{$email}', '{$bio}', " .
"'{$facebook_url}', '{$twitter_handle}');";
mysql_query($insert_sql);
var_dump(mysql_insert_id());
?>