Ok i am not sure if this signup script is good or not, this is my first try at it and it does work but their are a few questions i have if anyone can help?

1, Is this script right meaning is this script done right? or atleast ok?
2, Is their some way that i can make sure the email is a real email address and not just 1 letter or nonsense writing in it?
3, If this code is wrong can you tell me what is wrong with it?

Thanks!!!

<?php

$con = mysql_connect('localhost','aaaa','aaaa') or die (mysql_error());
$db = mysql_select_db('aaadatabase') or die (mysql_error());

$username  = $_POST['username'];
$password  = $_POST['password'];
$email        = $_POST['email'];
$submit      = $_POST['submit'];

$username = mysql_real_escape_string($username);
$password = mysql_real_escape_string($password);
$email = mysql_real_escape_string($email);

$error = false;
$message = "";

if(strlen($username) < 5) {
$error = true;
$message .= "<font color='#ff0000' size='2'><b>You did not enter a username.</b></font>";
}

if(strlen($password) < 8) {
$error = true;
$message .= "<font color='#ff0000' size='2'><b>Your password must be atleast 8 - 15 characters long.</b></font>";
}

if(strlen($email) < 1) {
$error = true;
$message .= "<font color='#ff0000' size='2'><b>You must enter an email address.</b></font>";
}


$sql      = "select user_name from users where user_name='$username' ";
$result   = mysql_query($sql);


    if($row = mysql_fetch_array($result)) {
    $error = true;
    $message .= "Sorry that username is already in use";
    
    } else {
    
    $sql = mysql_query("Insert into users (user_name, user_password, user_email) values ('$username' , '$password' , '$email') or die (mysql_error()");
    $sql2 = mysql_query("insert into books (user_name) values ('$username')");
    $result = mysql_query($sql);

    $error = true;
    $message .= "<font color='#ff0000' size='2'><b>Congratulations you are now a member please login.</b></font><br/><br/>";

    }
?>

Is their some way that i can make sure the email is a real email address and not just 1 letter or nonsense writing in it?

You can use regular expressions for this.
To get a better understanding of these, there is a great video tut going on now here:
http://blog.themeforest.net/screenca...s-for-dummies/

Otherwise, google for regular expressions email validation.

Is the actual form on another page?
And maybe swap a <span> for that <font>(deprecated).