Can an aircraft accommodate more than 800 passengers???

The Airbus A380 can!!! The A380, will be the largest airliner ever built. Lengthwise, it would nearly stretch from goal line to goal line of a football field while its wing tips would hang well beyond the sidelines. Three full decks will run along the entire length of the plane. Upper and main decks will serve as passenger areas, and will be connected by a grand staircase near the front of the plane and by another smaller staircase at the back. Although the lower deck will be reserved primarily for cargo, it could be outfitted for special passenger uses such as sleeper cabins, business centers or even child care service. In a one-class configuration, the A380 could accommodate as many as 840 passengers. The more likely three-class configuration will still offer an unprecedented 555 passenger seats.

Check this awesome flash site to read more about that. The project started in 1991 it is now on the testing phase.
http://events.airbus.com/A380/default1.aspx