If you have at least one level 90 job and all the Final Fantasy XI expansion packs and battle and scenario add-ons, you can apply to test out new content for Final Fantasy XI before it’s officially released to the public. Square Enix will allow a limited number of players to help test this content out on a Final Fantasy XI Test Server.
“Along with the launch of the test server, a new World ‘Undine’ will become available,” a Final Fantasy XI community moderator revealed. “You can copy your character data in the game over to ‘Undine’ and be able to try out new content.”
You can read more details about how to sign up for the Test Server here.