HTML switch- template thing

[xenooreo]

Hey folks!
I have a bit of a problem, I don't think it's too horrible of one though.
I really hope the PHP gurus here will bless me with their assistance ^^

My site does use PHP, and I am semi-familiar with it. It uses includes and loads content into the main template, etc, etc.

Now the most important thing is, I wish to have user selectable templates for the site. At the moment, I sort of have that. A php snippet swaps the CSS stylesheet that is used, so the general look changes. But I want more than that; I would like the entire HTML to be able to be swapped, so that I can change entire div and table groups, images, the whole layout, etc etc, instead of having the same general layout that simply is displayed differently. For example, something that resembles some of the CMS template systems such as mambo or joomla.

So yeah, in a nutshell, I need switchable templates. Can somebody point me in the right direction?