1. Get the latest version at http://dev.bukkit.org/server-mods/my-worlds/
2. Set it up the usual way
3. Make sure the Nordic.jar is loaded
4. use the /create command to create a new world. For Nordic the command could look like this:
/world create my_epic_nordic_world:Nordic: i_haz_uber_seed
My Worlds should now create a new world named my_epic_nordic_world using the Nordic generator with the seed i_haz_uber_seed. Now you can use the world like you're used to
Getting a problem with the "Tropic" one, I say /world create Tropic:Tropic On log and chat it says "Preparing to generate (Tropic)" or something like that but, It won't start generating! I wait an hour an it just won't generate!!!!