If you want to check out the exciting new features in Joomla! 1.5 in a completely safe environment then this is the tool for you. The CD is a fully working webserver etc and everything runs from the CD. There is nothing to install. The only files written to your hard drive are temporary files and these are removed as soon as you quit the browser. You can play with the beta to your hearts content and no matter what you do it won't break. As soon as you quit the web browser everything is reset