?! уточни - каким стрелочкам?
<!DOCTYPE HTML>
<html>
<head>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.js"></script>
</head>
<body>
<input type="text">
<script>
$('input').keypress(function(event){
if (event.which < 48 || event.which > 57) return false;
});
</script>
</body>
</html>