The first beta of Demigod is looking to be on September 5th. We wanted to do it at the end ofAugust but we're all going to be attending PAXX (Penny Arcade trade show) that week and we want to be here to help people get started.
Now, just so you know, the first beta we are intentionally removing a lot of gameplay elements just so that we can get people to focus on compatibility and performance. We want this game to be about twice the performance as Supreme Commander had (a LOT of work has gone into lowering the hardware requirements). Multiplayer in the initial beta will be LAN only but you'll be able to play against an AI player.
Once we have all that nailed down, we can add the actual gameplay elements, broaden the multiplayer, and go from there.