Add a new theme?

[blueskyler]

I was wondering how to add a new theme because when I add one, it shows up on the change theme page and in the admin cp, but when I select "Use this theme", it doesn't change at all, and uses the default theme. The only way I can get it to work is by putting the style.css in the other theme's folder, but then I still only have one theme. Can anybody help me with this?