Fijate si esto te sirve...
Código:
<html>
<head>
<title> Solo numeros </title>
<script language="JavaScript">
<!--
var nav4 = window.Event ? true : false;
function acceptNum(evt)
{
// NOTE: Backspace = 8, Enter = 13, '0' = 48, '9' = 57
var key = nav4 ? evt.which : evt.keyCode;
return (key <= 13 || (key >= 48 && key <= 57));
}
//-->
</script>
</head>
<body>
<input type=text name="valor" size=12 maxlength=12 onKeyPress="return acceptNum(event)"><br>
</body>
</html>
<hr noshade size=1><img src="http://www.gograph.com/Images-8712/ClipArt/cat03.gif" height="50" border=0 align="absmiddle"> <font size="2" face="verdana" color="#000000">
bet[/CODE]