Copy the following into Master Page of each site collection that you want this global navigation to appear. This should go between the <head></head> code.
<script type="text/javascript" src="http://Scripts/jquery-latest.min.js"></script>
<script type="text/javascript" src="http://Scripts/jquery.SPServices-latest.min.js"></script>
<script type="text/javascript" src="http://Scripts/topnavigation.js"></script>