I want people to go to www.site.com, but have it pull data from /public_html/mysite

I want people to go to www.site.com, but have it pull data from /public_html/mysite and not from /public_html/

Is this possible?

If your server is running apache, I'm pretty sure this can be accomplished using .htaccess--of which I unfortunately know precious little myself.
This tutorial should get you on your way: Comprehensive guide to .htaccess (http://www.javascriptkit.com/howto/htaccess.shtml) (from JavaScriptKit).

I believe the line you need is
Redirect / http://www.mysite.com/mysite