I'm working on a design, and in it there will be no public login, no publicly submitted reviews, the only thing users will be used for are the forums and the comments. What will be public is the news, articles, reviews, etc...

The way I wanted it was so everything would be done by myself and a couple friends so in essence, to the public, the inner-workings of the site are unknown to them.

This brings me to my question, if I was to have admin.php (and all admin-related modules) use one theme/template, and everything that I made public use a separate theme/template, how might I go about doing this?

I'm just worried that if I take the entire theme and scrap everything, including the side dynamically-driven navigations (because I plan to use a static navigation on the public theme) I'll lose that in the admin area - which would make it useless.

Thanks.

Have you tried XOOPS yet? If you did, you would notice that admin uses its own theme (non-smarty hard-coded).
I don't think you should concern messing up themes. Give a spin and you would know for sure.

If I understand the request (correct me if I'm wrong) he wants a primarily public anon server with only a handful of users delegated to maintaining content.

Can do. I just started a site with a similar need. You won't need things like the Login block but still want the ability to login. If you want users to actually login for the Forums you can place the login block only on the Forums page. Or any number of things.

If you don't like how the Main Menu looks or functions (but it is very flexible) you can not show it and use perhaps a custom block with your preferred hardcoded menu.

Lots of ways to make it look like a static site but have the CMS functions less obvious. There are some outstanding webmasters around this site who can point you to some of their work.

Have a look at this story. This guy has done an outstanding job of using the XOOPS backend without making it look like a "typical" XOOPS site, if there is such a thing :)
BTW, you can still login to a XOOPS site without having a login block on the front page: Just go to http://www.yoursite.com/user.php and you get the login area. And then you go to http://www.yoursite.com/admin.php for the admin menu.
There's another post somewhere where somebody did a site using inline frames, but I can't find it. :(