Close but no cigar. I will expand this a bit.

N900 = Maemo 5 = Fremantle = Maemo Core + Fremantle UI
N9 (?) = Maemo 6 = Harmattan = Maemo Core + Harmattan UI + MeeGo compatibility layer
MeeGo = MeeGo Core + reference UX (no vendor ships this and is this probably not the one you want)
The next Nokia MeeGo device = MeeGo Core + (Harmattan + 1) UI
This thread = Harmattan-meets-N900-but-has-no-specific-name = MeeGo Core + Harmattan UI

In other news - it would be really-really cool to hear something about the Harmattan SDK, it was supposed to be 2010Q1, we're now Q3, and even though I know MeeGo caused a stir *some* info about what's going on would be welcome.