How can i program in php to show a box as a pop up in same window.?

I am thinking about pop ups that can seen on yahoo site. please help me. I think some times it can use layers to do this.

How can i program in php to show a box as a pop up in same window.?
%26lt;a href=""


onmouseover="var pop = document.getElementById('pop');


pop.style.display=''"


onmouseout="var pop = document.getElementById('pop');


pop.style.display='none'"


%26gt;Show/Hide%26lt;/a%26gt;


%26lt;div id="pop"


style="position:absolute;


top:100px;


left:200px;


display:none;


border:1px dotted black;


width:100px"%26gt;Hello%26lt;/div%26gt;