Hey Greg,
You can make a tab the default by editing ProductDetails.ascx on lines 98-101 change the following code:
//When page loads...
$(".tab_content").hide(); //Hide all content
$("ul.tabs li:first").addClass("active").show(); //Activate first tab
$(".tab_content:first").show(); //Show first tab content
to this, change the highlighted 3 to whichever tab you want to display as default, make sure to change both 3's.
//When page loads...
$(".tab_content").hide(); //Hide all content
$("ul.tabs li:nth-child(3)").addClass("active").show(); //Activate second tab
$(".tab_content:nth-child(3)").show(); //Show second tab content
Christian