I’ve been away from web design for almost 2 years and I can’t believe how much I forgot. Could someone give me a quick refresher:
The main page (home page) for the site is supposed to be labeled main.html (or main.htm)?
If I’m using Wordpress, do I install that to the root directory in my hosting control panel? IE. do I install it to /root or root/wordpress?
The home page is usually index.html or index.php or similar.
When you install WordPress you can choose either of those options. When you go into the settings you can tell it what URL to use.
If you’re building a traditional static site your home page should be named index.html
In addition to what felgall and amichel86 already told you about naming the homepage. The index.html, .php or whatever extension you are using, should be usually indeed placed in the root. I’m not familiar with Wordpress so I can’t give you an answer too that. But I’m sure that should be mentioned in the help files that normally comes with the CMS.
If he’s using Wordpress, by default in the Twenty Ten theme there should be an index.php file that calls the header, the loop, the sidebar and the footer. 
Yes. to /root
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Actually it doesn’t matter how you name your homepage, but it is like a standard to be named “index.html” or “index.php”