Can get active navitab function to highlight right tab if using php includes?

[needinghelp]

Hi.  I'm trying to use a set of navitabs (tabs?) within a php includes menu.  Before I moved the navitabs to an 'included' php file, it it was setup to change the colour of the index/welcome tab by using  class="activenavitab"  function.  Now, my problem is that I don't know how to code the simple navitabs.php file to automatically change the highlighted tab to whichever page is being shown.  Is this even possible?

You can see what I mean if you view the basic template I found.  I uploaded it (including my simple changes so far) to http://www.buymicroworms.com/possibleglasssitedesign/indextesting.php.  You can see the welcome tab highlighted.  But if you click on the Bio tab, it brings up the bio page but the welcome tab remains the highlighted tab (because that's the one set to activenavitab in the navitab.php file).  Is there some way I can change the navitab.php file to automatically highlight the active tab?  If at all possible, I would like to do this so I will be able to quickly edit the menu as I expand the site (once I start making the REAL version of the site...still just working on the template at the moment).

Thanks!!!