soniclord, как вариант...
<!DOCTYPE html>
<html>
<head>
<!--
<script src="http://code.jquery.com/jquery-latest.js"></script>
<link rel="stylesheet" type="text/css" href="tmp.css" />
-->
<style type="text/css">
</style>
<script type="text/javascript">
function inc() {
var o=document.getElementById('box');
o=o.getElementsByTagName('span')[0];
o.innerHTML=-(-o.innerHTML)+1;
};
</script>
</head>
<body>
<div id='box'>
<span>1</span>
</div>
<button onclick='inc();'>+</button>
</body>
</html>