Just use jquery
First include jquesy js file in your page they try this code
<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript">
function show_data()
{
$.post("another.php",function(data){
$("#data_div").html(data);
});
}
</script>
<input type="button" values="Click" onclick="show_data()">
<div id="data_div">
</div>
</input>
The contents that are executed in another.php will be seen in the division having id data_div