Unfortunately, the only way I know of to acquire the demo is on the PC Gamer disc, although I'm willing to bet it can acquired through other sources.
Naturally, I wouldn't make such a topic without some pics:

Opening screenie from tutorial. I prepare to select Rufus, a Norman general.

My archers fire on the Saxon dogs.

Armoured Seargents prepare to skewer some Saxons.

Battle of Agincourt: Some French Knights charge the line of my English army.

Battle of Agincourt: An overhead view showing the scale of battle. My army of 1,000 squared off against a force of about 1,500.
The demo ran pretty smooth on my system (Athlon 64 X2 4400+ and Radeon X1950XTX) at 1280 x 1024 with antialiasing and anisotropic filtering on. One thing I noticed that I liked was that there appear to be several character models for each unit, so each soldier in a unit doesn't look exactly identical.
I can't wait for this game.