input der kun må indeholde talværdier

Det kan man ikke
http://www.ncdesign.org/html/050form.htm#basic
\"<input type=* name=**>
*=text, password, checkbox, radio, image, hidden, submit, reset
**=Symbolic Name for CGI script\"

Du kan kode dig ud af det.
<html>
<head>
<title>Untitled Document</title>
<meta http-equiv=\"Content-Type\" content=\"text/html; charset=iso-8859-1\">
<script type=\"text/javascript\">
function tjek(el){
    str = el.value;
    if (window.event.keyCode > 65 || window.event.keyCode < 222){
        if (str.length > 0){
            str = str.slice(0, str.length - 1);
            el.value = str;
        }
    }
}
</script>
</head>

<body onkeydown=\"alert(window.event.keyCode)\">
<input type=\"text\" onkeyup=\"tjek(this)\">
</body>
</html>

ups
<html>
<head>
<title>Untitled Document</title>
<meta http-equiv=\"Content-Type\" content=\"text/html; charset=iso-8859-1\">
<script type=\"text/javascript\">
function tjek(el){
    str = el.value;
    if (window.event.keyCode < 48 || window.event.keyCode > 57){
        if (str.length > 0){
            str = str.slice(0, str.length - 1);
            el.value = str;
        }
    }
}
</script>
</head>

<body>
<input type=\"text\" onkeyup=\"tjek(this)\">
</body>
</html>

Denne er pænere, og virker i alle browsere.
<html>
<head>
<title>Untitled Document</title>
<meta http-equiv=\"Content-Type\" content=\"text/html; charset=iso-8859-1\">
<script type=\"text/javascript\">
function tjek(el){
    str = el.value;
    myreg = /\\D/;
    str = str.replace(myreg, \"\");
    el.value = str;
}
</script>
</head>

<body>
<input type=\"text\" onkeyup=\"tjek(this)\">
</body>
</html>