log-out with a pop-up windows

hi
where can i insert the code in order when a user log-out a windows will popup?

please advice.

In the template bit find the logout link and change it to
<A HREF='javascript:window.alert("Popup window on logout link");'> logout </A>
or for a confirm box

<a href="logout.php" onclick="javascript:return confirm('Are you sure you want to logout?')">logout</a>