Hello World with jQuery :
<html>
<head>
jQuery Hello World
<script type="text/javascript" src="jquery-1.4.2.js">
</head>
<script type="text/javascript">
$(document).ready(function(){
$("#flag").html("Hello World !! (display due to jQuery)");
});
</script>
<body>
<font color=red>
Hello World !! (display due to HTML)
</font>
<font color=blue>
<div id="flag">
</div>
</font>
</body>
</html>