Hvordan omdøbe billedfil efter $id ved upload til server?

Mit spørgsål lyder:
Hvordan omdøber jeg en billedfil, som jeg har uploadet via en form, filen bliver uploadet til folderen "images" og tilhørende data skrives i MySql-db.
Hvis nu $id bliver f.eks. 55 og der bliver uploadet en .jpg-fil, skal dette billede altså omdøbes til 55.jpg og dette nye navn skal så fremgå i rækken i mysql-db'en.

Min kode ser pt. sådan her ud:

<?

if(isset($_POST['upload']))
{
        $target = "images/";
        $target = $target . basename( $_FILES['userfile']['name']);
        $fileName = $_FILES['userfile']['name'];
        $tmpName  = $_FILES['userfile']['tmp_name'];
        $fileType = $_FILES['userfile']['type'];
        $fileSize = $_FILES['userfile']['size'];
        $companyname = $_POST['companyname'];
        $department = $_POST['department'];
        $address1 = $_POST['address1'];
        $address2 = $_POST['address2'];
        $country = $_POST['country'];
        $contactname = $_POST['contactname'];
        $phone = $_POST['phone'];
        $fax = $_POST['fax'];
        $email = $_POST['email'];
        $website = $_POST['website'];
        $fileNameny = str_replace(" ","_",$fileName);
        $fp = fopen($tmpName, 'r');
        $content = fread($fp, $fileSize);
        $content = addslashes($content);
        fclose($fp);
       
        if(!get_magic_quotes_gpc())
        {
            $fileName = addslashes($fileName);
        }
       
        $tmpName = $_FILES['userfile']['tmp_name'];
       
        list($width, $height, $type, $attr) = getimagesize($tmpName);
       
        if($width>235 || $height>130)
       
        {
            die("Exceeded image dimension limits: width= 235px height= 130px.");
        }
       

              // Connects to your Database
              mysql_connect("ip-address", "user", "password") or die(mysql_error()) ;
              mysql_select_db("database") or die(mysql_error()) ;
       
        $query = "INSERT INTO tabel (name, type, size, companyname, department, address1, address2, country, contactname, phone, fax, email, website ) ".
                "VALUES ('$fileNameny', '$fileType', '$fileSize', '$companyname', '$department', '$address1', '$address2', '$country', '$contactname', '$phone', '$fax', '$email', '$website')";

        mysql_query($query) or die('Error, query failed');
        //Writes the photo to the server
        move_uploaded_file($_FILES['userfile']['tmp_name'], $target);       
       
//        mysql_close($conn);
       
        echo "<br>Logo: <b>$fileNameny</b> uploaded
        <br> (type: $fileType - size: $fileSize)
        <br>Company name: <b>$companyname</b>
        <br>Department: <b>$department</b>
        <br>Address line 1: <b>$address1</b>
        <br>Address line 2: <b>$address2</b>
        <br>Country: <b>$country</b>
        <br>Contact name: <b>$contactname</b>
        <br>Phone: <b>$phone</b>
        <br>Fax: <b>$fax</b>
        <br>Email: <b>$email</b>
        <br>Website: <b>$website</b>";
}       
?>