I'm having a very basic problem: I'm trying to create a new theme for a wordpress installation locally on my computer.

I've created a styles.css and index.php file and put it in a folder in wp-content/themes. But it doesn't appear in the Wordpress themes page. 

As a test, I made a change to the description of one of the existing themes (Twenty-Ten) in its style.css, and refresh the Wordpress themes page, but the old description continues to be shown. This suggests to me that I'm simply using the wrong folder, but that's not possible! Any ideas on this problem much appreciated.

UPDATE: In fact, even when I delete Twenty Ten from the Themes folder, it's still available as an option in the Wordpress backend, and I can activate it... Very strange...

G