Wahtel,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script>
<script>
$(function(){
var $add = $("#add"), indx = 1;
$add.click(function() { indx++
$('[name$="[word]"]').last().clone().appendTo('body')[0].name = 'linkbuilder['+indx+'][word]';
$('[name$="[link]"]').last().clone().appendTo('body')[0].name = 'linkbuilder['+indx+'][link]';
alert($('body').html())
});
});
</script>
</head>
<body>
<input id="add" name="" type="button" value="add">
<input name="linkbuilder[1][word]">
<input name="linkbuilder[1][link]">
</body>
</html>