MeeGo-Harmattan is going to be the bastard child of MeeGo Handheld UX and the existing Maemo back-end, as I understand it. Personally it's horribly confusing, and I'd just as soon ignore it when talking about MeeGo, since it's not -part- of MeeGo.

The MeeGo Handheld UX coming later will go on top of the MeeGo core that currently has only a console.