Head of the page, something like:
<script>function open_google(){window.open('http://www.google.com'); return false}</script>
Custom alert:
<a href="javascript: void(0)" onclick="create_alert('Custom alert containing link to Google', '<a style=color:red href=javascript:void(0) onclick=parent.open_google()>This</a> link opens Google in a new tab or window'); return false">custom alert</a> (
demo)
(for