My boss has a wordpress site
Ah, so many stories start this way.
You don’t, of course, want to edit core WP files; if you do, you will lose the changes when you update, among other issues. Modifying WordPress core files
Why not use the existing post/page editor and a plugin that will make it easy for him/her?
http://wordpress.org/extend/plugins/search.php?q=vzaar
If you want to keep him/her out of the post/page editor, try http://wordpress.org/extend/plugins/advanced-custom-fields/ to add your own meta and text editor boxes.