Funky J pointed out on RHL that the official Myth III site has updated with a downloadable multiplayer demo. The single multiplayer map included is called Ramparts, which accommodates 2 to 16 players, from both Light and Dark Armies and includes 7 of Myth IIIТs 14 multiplayer modes, from MythТs famous Steal the Bacon mode to a series of new multiplayer options developed by MumboJumbo.

You should also check out Myth Guide, a brand new website dedicated to the entire Myth series. Myth Guide launched with a Myth III demo page, which includes links to all known mirrors at this time.