Ted,
sorry, no demo avialable for Moo3 - thats what the Developers has stated all through development.
But chances are, if you like Galciv, you will like Moo3 as well, them being in the same genre and all.
Moo3 only focuses a bit more on tactical combat between fleets, and is geared a lot towards war-mongering.
At least, that is my impression, also based on the two previous games.
But all in all, a good 4x strategy game, which for myself will come in handy, when I've played Galciv to death, to amuse myself with for a few hours, before taking up the gauntlet and crushing those dratted Drengins once more
/Flemming