<html>
<head>
</head>
<body>
<input type="text" name="ik_payment_amount_usd" value="2.00">
<input type="hidden" name="kurs" value="51">
<input type="text" name="ik_payment_amount">
<div id="money-rub"></div>
<script>
get=function(sel){return document.getElementsByName(sel)[0]}
window["money-rub"].innerHTML=get("ik_payment_amount").value=(+get("ik_payment_amount_usd").value*get("kurs").value)
</script>
</body>
</html>