PHP echo to display javascript alert

Hi people, I’m very new to PHP and I want to put a javascript alert within a php thingo. The code I have looks like this:

 
$the_email = false;    
if(eregi("^[A-Z0-9._%-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$", $_POST['email'])) {
 $the_email = true;
} else {
 
echo "<script language=javascript>  alert('Please enter a valid email address, or I will kill you); </script>"; 
 
 $the_email = false;
}
if(!$the_email || !isset($_POST['name']) || !isset($_POST['message'])) {
 
echo "<script language=javascript>  alert('Please enter your '+fName); </script>"; 
 
}

Can anyone see anything wrong with this? Any feedback would be appreciated.