Well, the Templates and Add-ins dialogue is for loading global templates and add-ins. Here is what the Microsoft support site says:
"Templates can store styles, AutoText entries, AutoCorrect entries, macros, toolbars, custom menu settings, and shortcut keys. Loading a template makes it available as a global template (global template: Stores macros, AutoText entries, and custom toolbar, menu, and shortcut key settings that you can use while you work with documents based on any template. By default, the Normal template is a global template.). "
http://office.microsoft.com/en-us/word-help/about-loading-and-unloading-global-templates-and-add-in-programs-HP005186027.aspxNote that there is no mention of margins, header/footer or other pre-defined text. That's just not the way it works.
You could start a new document based on your template, then copy and paste the text from the file you've received into that new document, then go through and apply the styles.
cheers, teylyn