Web Error!!

[Forgiven]

So I am using Web Site Stuart 0.6 Beta
I edit all the files I need to but when i visit it I get this error.

Fatal error: Call to undefined function mssql_connect() in C:\xampp\htdocs\testing\config.php on line 2

I dont know whats wrong, I looked into my config.php it looks all right.

<?php
mssql_connect("******\SQLEXPRESS","sa","******");
mssql_select_db("GunzDB");
$opened = 1;
if($opened == 0){
    $pagetitle = "Server in maintenance";
}
?>

Can anyone help me? :) Would be greatly appreciated!

[MentaL]