Words in variables?

[Dakkar]

I made a registration form like this.But i want it to not accept any username which has remote or syl words inside of it how can i do it?

<?

@mysql_connect("localhost", "dakkar", "1234567")
or die("Couldnt connect with database!");
@mysql_select_db("test")
or die("An error occured in database");

$sql = "SELECT count(*) FROM kayit WHERE username = '".$_GET['u_name']."'";
$res = mysql_query($sql) OR die(mysql_error());
$row = mysql_fetch_row($res);

if($row[0] == 0) {
if (($u_name !== "") && ($pass !== "") && ($mail !== "")) {
if (ereg("@",$mail) && ereg(".",$mail)) {
@("insert into kayit values('$u_name','$pass','$mail')");
echo "<center><b>Thanks for joining us.</b></center>";
} else {
echo "<center><b>Please enter a valid email adress</b></center>.";
}
} else {
echo "<center><b>Please fill all the blanks.";
}
} else {
echo "<center><b>The username you want is already registered.</b></center>";
}
?>

[Merve]

[man]preg_match[/man]

[Dakkar]

How can i use this for example can i use this like this ?

if (preg_match ("$u_name", "Administrator.")) {
echo "This is a forbidden username.";
} else {
echo "You can use this username.";
}