No. to enable user to use MOC 2007 you need to enable enhanced presence.
But, if you enable enhanced presence for a user and this user login on MOC 2005 there are no problems, but if this user login a first time in MOC 2007 he can't log more in MOC 2005.
So don't permit which the migrated users login on MOC 2007 before you have upgrade his client.
Bruno Estrozi - MCSE/MCTS/MCITP - Unified Communications Specialist | http://brunoestrozi.spaces.live.com