CODE
<?php
//This retrieves the ip of the user
$ip=getenv('REMOTE_ADDR');
//Insert the user's IP here
$banned=xx.xx.xxx;
if (ereg($banned,$ip)) {
echo 'Banned';
exit();
}
?>
//This retrieves the ip of the user
$ip=getenv('REMOTE_ADDR');
//Insert the user's IP here
$banned=xx.xx.xxx;
if (ereg($banned,$ip)) {
echo 'Banned';
exit();
}
?>
There you go
simple IP banning. Of course you can also change what it echo's in this case when the user with that IP comes to the site it will say Banned. You could fool them by saying like site is down but I prefer huge red letters 
this tutorial was made by someone on my staff.