Submit = enter but same page calling

[system]

I want the form to be submitted when pressed enter...
This is what I got already
...

<script language="JavaScript"> 
NS4 = (document.layers) ? true : false; 

function checkEnter(event) 
{ 
	var code = 0; 

if (NS4) 
	code = event.which; 
else 
	code = event.keyCode; 
if (code==13) 
document.search_type.submit(); 
} 
</script> 

<form name="search_type" method="post" action="<?php echo($PHP_SELF) ?>">
<tD width="250">Enter a typename of part of a type</tD>
<tD><input name="search_type" type="text" maxlength="30" onKeyPress="checkEnter(event)"></tD>
<td><input name="submit" type="submit" value="Search"></td>
<tD width="250">Use <strong>%</strong> as a wild card (same as *)</tD>
</form>

So far I think it's good, but now comes the tricky thing...

if ($HTTP_POST_VARS["submit"]=="Search")
{ $error = search_data($HTTP_POST_VARS);
  if ($error == ""){
    $success = "Search completed" ;
	}
	else {
	print $error;
	}
}

How can I let the same page know the submit button==Search ???

Hope you guyz can help me...

I would really appreciate it

[FrozNic]

instead of checking to see if submit == search do this:

check to see if submit == true

if it's been submitted it will return true.. else it won't.

[system]

I changed it to true but still same result...
it empties the field but doen't do anything else... 🙁
any other suggestions?