It depends on the features you want in a MMORPG. If you want terrain paging, you're looking at a major code overhaul. You'll have to do some netcode massaging as well to accommodate more players with less accuracy (since you don't need the collision accuracy of an action title). Do a search of MMO games within in the forums and see what others are doing. Mostly it requires either a majorly massive code overhaul or a minorly massive code overhaul depending on the featureset you desire.
Associate David Montgomery-Blake
David MontgomeryBlake