If one block has content do not show other block I have a region in my page.tpl.php file called "seminars", and it has two blocks (views) assigned to it, one is called "view_upcoming_seminar" and the other is called "testimonials". The content shows up great for both blocks (views) in the region. What I'd like to do is only show "testimonials" if there is no content in "view_upcoming_seminar".  

I'm just not sure what the best approach is, and any pointers in the right directions would be grand!
Open the "Advanced" section on the "view_upcoming_seminar" View settings page, and add a "No results behavior" of type "Global: View area". Point it to your "testimonials" View.