Login Form Help (I'm a php noob)

[Advocation]

http://paste.devpipe.com/1514

Whats wrong with the code above? It works untill it has to query the database.. The mysql connection script is working fine so its something to do with this script!

Thanks

[Junkfee]

$sql = mysql_query("SELECT * FROM tblUsers WHERE username = '".$username."' and password = '".$password."'") or die(mysql_error());

$row = mysql_fetch_array($sql);

if(mysql_num_rows($sql) < 1) {
echo 'Sorry, user not found';
}else{
echo 'Success';
}