what i want to do is give EACH person there OWN 4 digit code that increments by 1 every time someone NEW signs up and it starts at 0001 and ends at 9999 how can i do this with the script i have?

gistfile1.php

<?php
$host     = "**********"; // Host firstname
$name     = "****************"; // Mysql userfirstname
$password = "***********"; // Mysql password
$db_name  = "************"; // Database firstname
$tbl_name = "users"; // Table firstname
// Connect to server and select database.
mysql_connect("$host", "$username", "$password") or die("cannot connect");
mysql_select_db("$db_name") or die("cannot select DB");
// Get values from form
$firstname         = $_POST['firstname'];
$lastname          = $_POST['lastname'];
$email             = $_POST['email'];
$resumewebsitename = $_POST['resumewebsitename'];
$website           = 'http://www.thorbis.com/onlineresumes/users/' . $resumewebsitename;
$email             = mysql_query("SELECT * FROM users WHERE email='$email'");
if (mysql_num_rows($email) > 0) {
                echo "Sorry That Email Has Been Taken Please Try Again :D";
} //mysql_num_rows($email) > 0
else {
                $dbunames = mysql_query("SELECT * FROM users WHERE website='$website'");
                if (mysql_num_rows($dbunames) > 0) {
                                echo "Sorry That Resume Name Has Been Taken Please Try Again :D";
                } //mysql_num_rows($dbunames) > 0
                else {
                                // function to recursively copy
                                // a directory and its subdirectories
                                function copyRecursive($source, $destination)
                                {
                                                // check if source exists
                                                if (!file_exists($source)) {
                                                                die("'$source' is not valid");
                                                } //!file_exists($source)
                                                if (!is_dir($destination)) {
                                                                mkdir($destination);
                                                } //!is_dir($destination)
                                                // open directory handle
                                                $dh = opendir($source) or die("Cannot open directory '$source'");
                                                // iterate over files in directory
                                                while (($file = readdir($dh)) !== false) {
                                                                // filter out "." and ".."
                                                                if ($file != "." && $file != "..") {
                                                                                if (is_dir("$source/$file")) {
                                                                                                // if this is a subdirectory
                                                                                                // recursively copy it
                                                                                                copyRecursive("$source/$file", "$destination/$file");
                                                                                } //is_dir("$source/$file")
                                                                                else {
                                                                                                // if this is a file
                                                                                                // copy it
                                                                                                copy("$source/$file", "$destination/$file") or die("Cannot copy file '$file'");
                                                                                }
                                                                } //$file != "." && $file != ".."
                                                } //($file = readdir($dh)) !== false
                                                // close directory
                                                closedir($dh);
                                }
                                $source_directory      = "Interactive Resume/";
                                $destination_directory = "users/";
                                copyRecursive($source_directory, $destination_directory);
                                rename("users/user", "users/" . $resumewebsitename);
                                $to      = "bcw1995@gmail.com";
                                $subject = 'hi';
                                $message = "Name: " . $firstname . "<br>" . "Last: " . $lastname . "<br>" . "Email: " . $email . "<br>" . "Website: " . $website . "<br>" . "Pin: " . $pin;
                                $headers = "From: $from\r\n";
                                $headers .= "Content-type: text/html\r\n";
                                if (mail($to, $subject, $message, $headers)) {
                                                echo ("<p>Since You Have Used My services I will get an email stating that you have filled out this form and i will contact you back within 6 hours of you submiting the form!</p>");
                                } //mail($to, $subject, $message, $headers)
                                else {
                                                echo ("<p>I dident get a message stating that you have filled out the form can you manualy send me your email and info so i can customize your website please my email is bcw1996@gmail.com thank you :D</p>");
                                }
                                // Insert data into mysql
                                $sql    = "INSERT INTO $tbl_name(firstname, lastname, email, website)VALUES('$firstname', '$lastname', '$email', '$website')";
                                $result = mysql_query($sql);
                                // if successfully insert data into database, displays message "Successful".
                                if ($result) {
                                                echo "Successful";
                                                echo "<BR>";
                                                echo "This is your new resume site i will edit it with your info ASAP once i have contected you: " . $website;
                                                echo "<BR>";
                                                echo "<a href='http://www.thorbis.com'>Back to Home Page</a>";
                                } //$result
                }
}
?>

add this after mysql_select_db();

foreach($_POST as &$v)
    $v = mysql_real_escape_string($v);

this will prevent the possibility of sql injections through data that are sent by post http method

is there anything else i should fix?