The "Exclusive" tag means exactly that—certain features, maps, skins, and server access are locked to this specific build. You cannot get the IMC experience from a generic Eaglercraft launcher found on a random forum.
It seems that Eaglercraft IMC Exclusive is not an officially recognized version of Minecraft by Mojang Studios, the game's developers. Instead, it appears to be a community-created, modded version of the game.
Players can join dedicated servers or invite friends to their single-player worlds using peer-to-peer "Shared Worlds".