I would use the disable property on a onclick event.
<html>
<head>
<script type="text/javascript">
function disableOption()
{
document.getElementById("but").disabled=true;
}
</script>
</head>
<body>
<form>
<input id="but" type="button" onclick="disableOption()" value="Disable">
</form>
</body>
</html>
