There's a micro-atx model board in the case seen in the photo there. If the 900 has been revised since last July hopefully they increased the depth a little since that gap will be closed right up behind the 5 1/4" drive bays with a full size atx board. Tight space when going to use round ide cables for two ide drives here(one optical).
Looks more like an AT style being thinner since the Asus model board reaches the next row of fastener holes! You won't be as cramped using any round ide cables there however.