Mine

<html>
<head>
<title>
</title>
<script type="text/javascript">
var fieldcount=1;
function addAuthor(){
fieldcount++;
var newAuthor=document.createElement('input');
newAuthor.type=text;
newAuthor.name='author'+fieldcount;
newAuthor.id='author'+fieldcount;
document.getElementById('fs').appendchild(newAuthor);
}
</script>
</head>
<body>
<input type="text" name="firstAuthor" id="firstauthor">
<fieldset id="fs">
<button onclick="addAuthor(); return false;">
</fieldset>
</body>
</hmtl>