Be advised that WordPress 2.9 MU is no longer a separate project from the main WordPress branch. It is continuing development as part of the main WordPress 3 branch under the name ‘multi-site’ or MS. This means that you can get all the benefits of both WordPress and WordPress MU versions by using the latest WordPress version. To help you in the process of creating a multi-user website with the latest WordPress version we have created a detailed step by step WordPress multi-site tutorial available here.
You can easily create a back up of your WordPress website by simply downloading all of your WordPress files via FTP and export your database. You can access your WordPress files and download them via FTP following the instructions in our great FTP Video Tutorial.
Your blog MySQL database can be easily exported via your cPanel -> phpMyAdmin following the instructions at our phpMyAdmin tutorial.
If you would like to start your WordPress MU Blog in a few clicks, check the WordPress MU Hosting package.