<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="ru" lang="ru">
<head>
<title></title>
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8" />
</head>
<body>
<div>
Сюда можно вводить только цифры.
<input id="my" />
</div>
<script type="text/javascript">
document.getElementById("my").addEventListener("keypress", function(e){
if (!e.keyCode || e.keyCode<48 || e.keyCode >57) e.preventDefault();
}, false)
</script>
</body>
</html>
Works fine for me.