ive always wondered what the point of 2 graphics cards was. is it something to do with having two monitors? or does having graphics cards actually help?
SLi and Crossfire are two technologies where you link together two, (or now you can get up to four), graphics cards together inside your machine. You don't need two monitors, they just both contribute to the total processing power.
However, the performance gain isn't 100% and buying one graphics card of twice the power is still preferable to two. Also, the two cards must be exactly the same spec and be SLi compatible, (or Crossfire in the case of ATi chipsets), the motherboard must be SLi compatible, (SLi mode cannot be used on a Crossfire motherboard and vice-versa), and must have two slots compatible with graphics cards, (PCIEx32 or whatever).
As I say, you're generally better off buying a single graphics card of the highest spec you can reasonably afford and then, if the mood takes you, you can upgrade with a second card of the same spec in a couple of years maybe, (when the price of the card will be considerably less).
