Duplicating a MySQL Database

I would like to install a new version of a PHP/MySQL program (phpBB 2.0.x->phpBB 3.0 RC1 - my admins need to learn the new program before going live). The installer makes major changes to the MySQL database tables. I would like to do this on a copy of the database.

How do I duplicate an entire database using phpMyAdmin, hopefully in one easy step?