Hey Dave,
Yeah, it's always a bit of a learning curve the first time around creating your own website. Ultimately the question can have lots of answers as I understand, but this is what I'd start with:
1. Make sure Imagevue was uploaded to your DEFAULT folder. That is, your index.php should be in the 'top most' directory of your website. See below for more details.
2. Remove your index.html as most servers will look to the .html BEFORE a .php extension (as I understand).
I noticed your gallery is in it's own sub-directory, which is cool, but you need to tell your website to point to it as a default then. Personally, I'd move everything over to your default directory rather than creating subdirectories.
Your gallery is here:
http://www.davearndt.com/gallery/index.php
I'd move it here:
http://www.davearndt.com/index.php
I hope this helps!
Christopher