The new version of WordPress has many improvements including the new Themes structure. You can completely customize the appearence of your blog including the templates and switch between them with a click.
But the new theme structure doesn’t work with the old styles. To change an “style” to a theme, upload the style folder into the theme directory and open the style.css in a text editor. Insert the following template at the top and fill in the information.
<pre>
/*
Theme Name: Rose
Theme URI: the-theme's-homepage
Description: a-brief-description
Author: your-name
Author URI: your-URI
Template: classic
Version: a-number--optional
.
General comments/License Statement if any.
.
*/
</pre>
The important part is telling it to use the classic templates. Go to “Presentation” and select your theme and you back to normal.
A theme switcher is also available. Just drop it in the plugins directory and activate. Put <?php wp_theme_switcher()?> wherever you want the list to show up and you’re done.