function clearDefault(el) {
if (el.defaultValue==el.value) el.value = ""
}
// Then call this function using the 'onfocus' value of your input box:
<input value="Your Comment" onfocus="clearDefault(this)" type="text">
Paste this in your website: <script type="text/javascript" src="http://www.posteet.com/embed/1862"></script>