I’m working on a Wordpress plugin that allows you to switch themes on a per-post or per-page basis. That’s why this page looks different, I’m trying the plugin out here before releasing it.
The idea is that you upload a new theme into the usual Wordpress theme directory. You can use this theme for a single Post, a single Page or more of either. You specify which Posts/Pages are to use a theme other than the WP default by using a Custom Field. All you have to do is enter the theme’s name in the Custom Field value and the theme of that name will be used for the Post/Page it’s entered on.
I’m fairly sure there will be something like this out there already but when I tried to find a theme switcher all I could find was plugins that switched the whole theme.