ну мог бы в общем-то поэкспериментировать
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title></title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body>
<form>
<input id="textbox" type="text">
</form>
<div id="debug">
</div>
<script type="text/javascript">
var textbox = document.getElementById('textbox');
textbox.onkeypress = function( e ){
e = e || event;
var keyCode = e.keyCode || e.which;
if( keyCode == 13 ){
document.getElementById('debug').innerHTML += 'enter<br>';
return false;
}
}
</script>
</body>
</html>