Multiverse DOES NOT WORK. Nor do any other multiworld plugins. Cross-world TP'ing works in the latest builds.
Forge and bukkit have very different multiworld implementations. Bukkit has a separate world folder for each world, whereas forge stores them in <worldname>/DIM<number> - DIM0 for overworld, DIM-1 for nether and DIM1 for end. Along with that, each of those dimensions have the same name, meaning that on BukkitForge, worlds are named via their provider's name - overworld, the_nether and the_end. if you want mining ages, use mystcraft for now.