Just to offer some clarification, 99% of the time, video cards in laptops are actually integrated on the motherboard. So there isn't a card that you can pop out and pop a new one in. Hence, the reply. To get a better video card in a laptop, you need to get a better motherboard. And if you're going to that, you might as well buy a new laptop.
Alternatively, if you're looking to get in to serious gaming, like the previous poster mentioned, you may want to consider building your own desktop computer specifically for gaming and keep the laptop for everything else on the go.
Hope that helps. =)