With multiple AGP/PCI graphics cards, a person can split up the graphic from a computer game into multiple screens. This however, takes multiple computers, hence you need more than 1 AGP card.
2 AGP Video cards = 2 computers
4 AGP Vid cards = 4 comps
Notice how there are multiple computers on the ground without being used. Well, being used because the green light emitting diode is on, but they have the AGP cards that are giving the visual output information.
There is then software that breaks up the game display into multiple screens.