[KaVir]

You can't prevent OOC chitchat, the only question is whether you offer OOC channels within the mud itself, or if the players have to use an external application such as IRC or Skype.

But regardless of which option you go with, "implementing rules that force people to role-play" is the only way to prevent certain players from disrupting the roleplaying of others. These rules can be hardcoded, policed, or some combination of the two, but if you don't have any then the mud is "Roleplaying Encouraged", and will appeal to a different audience.