Are you able to have an external site load in the center frame of your website?

What I mean is, I want all the navigation bars on the left, top, right, etc to still be there, but the center frame (where most of the content loads) will be another site (like www.google.com), when a user clicks a link in the menu.

Thanks

Yep. Head to Admin > Static Menu Items and Content. On the creation of that, there's an option "If this is a link, load it in an inline frame?"