<form method="post" action="" enctype="multipart/form-data" onSubmit="registeruser()">
	<div>
		Username <span class="required">*</span><br/> <input class="registerinputbox" type="text" name="username" size="20"/><br/>
		Password <span class="required">*</span><br/> <input class="registerinputbox" type="password" name="password" size="20"/><br/>
		E-Mail <span class="required">*</span><br/> <input class="registerinputbox" type="text" name="email" size="20"/><br/>
		<input class="registerbutton" type="submit" name="registerbutton" value="Register"/> <span class="required">*</span> = required
	</div>
</form>


----------------------------------------------------------------------------

function registeruser() {
	if (document.getElementById("content").value == "") {
		return false;
	}

	if (window.XMLHttpRequest) {
		var xhr = new XMLHttpRequest();
	}
	else {
		var xhr = new ActiveXObject("Microsoft.XMLHTTP");
	}

	xhr.onreadystatechange = function() {
		if (xhr.readyState == 4) {
		  var posts = xhr.responseText;
		  document.getElementById("content").innerHTML = posts;
		}
		else {
			document.getElementById("content").innerHTML ='<img src="ajax-loader.gif"/>';
		}
	}

	xhr.open("GET", "registeruser.php");
	xhr.send(null);

	document.getElementById("content").style.display='block';
}

----------------------------------------------------------------------

<?php

$conn = blah;

$username = mysqli_real_escape_string($conn,strip_tags($_POST['username']));
$password = mysqli_real_escape_string($conn,strip_tags($_POST['password']));
$email = mysqli_real_escape_string($conn,strip_tags($_POST['email']));

if (strlen($username) > 15) {
	echo "The username you are trying to register is over the max of 15 characters, please go <a href='javascript:register()'>back</a> and try agian." ;
	die;
}

if (strlen($password) > 15) {
	echo "The password you are trying to register is over the max of 15 characters, please go <a href='javascript:register()'>back</a> and try agian." ;
	die;
}

if (strlen($email) > 35) {
	echo "The email you are trying to register is over the max of 35 characters, please go <a href='javascript:register()'>back</a> and try agian." ;
	die;
}

$sp_checkuserdb = "CALL checkuserdb('$username','$email')";
$rs_checkuserdb = mysqli_query($conn, $sp_checkuserdb);

$checkuserdb_result = mysqli_num_rows($rs_checkuserdb);
if ($checkuserdb_result >= 1) {
	echo $username;
	echo "The username or email you are trying to register is already in use, please go <a href='javascript:register()'>back</a> and try agian." ;
	die;
}

$conn = blah;

$sp_registeruser = "CALL registeruser('$username','$password','$email')";
$run_registeruser = mysqli_query($conn, $sp_registeruser);

echo "Thanks for registering, you may now login and begin posting!" ;

?>