Adding this manually to your own package is easy:
Create a <yourpackage>-header file and include this in all your pages (it works easier that way).
Within the header file include something like this:
<div id="subnavbar-div">
<div id="subnavbar-container">
<div id="subnavbar">
<div class="tab">
<a href=index>My Bookmarks</a>
</div>
</div>
</div>
</div>
where the tab is My Bookmarks. Obviously you can add more tabs in the subnavbar area. In addition to that you can even work with selected tabs (this is how my ETP enhancement works). I was too lazy to add the active tab function to my bookmarks header for the time beeing, but you can check it out for ETP if you are on HEAD and choose subnavbar as your application. Just create pages and you'll see what I mean.
For better documentation: /packages/acs-subsite/www/group-master
