Integrated graphics are pretty much crap; ok for general desktop and business use, but not very good for video and poor for gaming. A discrete graphics card is usually a replacement for integrated graphics, though some systems are starting to use both (the integrated graphics chip handling basic chores to keep heat down and conserve battery power, while discrete graphics take over for video and games). Early implementations of this required a switch be manually moved and the system rebooted to change video chips, but I think any system doing this now should be automatic. Generally, people looking at gaming class laptops are not primarily concerned with battery life, though, so I don't know if duel graphics would even be a feature in the laptops you are looking at.
