Do you ever feel like trying out a new WordPress Theme or hacking your present theme ... but you don't want to make your blog inaccessible - or worse yet, scrambled - while you are in the process of testing new themes.
This plugin is the answer to your prayers: Theme Test Drive by Vladimir Prelovac
Here's how to install and use it.
Download the plugin.

Unzip/extract using your favorite UNZIP utility. My current favorite is CAMUnzip

Upload the plugin folder to your /wp-content/plugins/ folder. I'm using WS_FTP.

In the WordPress dashboard, click the Plugins tab, find Theme Test Drive in the list of plugins, and click activate.

Now click the Presentation tab in the WordPress Dashboard. You will see a new sub-menu tab titled Theme Test Drive. Click Theme Test Drive, and choose the name of the theme you want to experiment with from the drop down list. Then click "enable".

Now when you click View site you will see your blog dressed up in the new theme. But you will be the only person seeing it that way.

All visitors to your site will still see your blog dressed in your currently active theme

When you are ready to go public with the new theme, click the Presentation tab, then the Theme Test Drive tab, and click Disable

Then click the Presentation tab, Themes tab, and set your newly designed theme as Current Theme

Cheryl:
I saw this but have not had a chance to check it out. Thanks so much for the post! Some great plugins are being developed now for Wordpress. One of my favorite blogs!