Is it possible to change the graphics card in a laptop and, if so, would a ATI Sapphire 1GB card run modern games on a Acer Aspire with 4GB DDR3 RAM, 500GB Hard Drive and AMD Athlon 2.4Ghz Dual-Core?

HD 5650 1GB ATI Mobility Radeon
4GB Ram
640GB Hard Drive
Core i3 330M

Game runs great on high/ultra with very little lag. Screen resolution is 1366 x 768. I am not sure about upgrading laptops, from what I hear most laptops aren't that great for upgrading.

So not great for upgrading that you basically can't. Sorry, if your current laptop is insufficient for gaming, you'll just have to make sure your next one is.

If you have a desktop computer, let us know.

From the top, the amount of VRAM attached to a discrete video card is about the least important specification to look at for performance judgment. Next, and your opening question, only the Sager brand's high quality desktop replacement machines offer any kind of ordinary CPU or GPU upgrades (Central Processor, Graphics Processor). All the rest, all brands, are welded into a single monobloc that no longer has any "inside" area to obtain access to.

Desktops remain the correct platform for game playing, although there are some more expensive laptops that are sold as game-capable. At least 95% of all mobile computer devices sold, moreover, do not have game-capable video included, which means the laptop buyer must take his time making sure he gets what he wants, instead of shopping simply on price and appearance.

With regard to discrete video graphics cards, core speed, VRAM speed, shader unit count, and memory system bandwidth are the key specs to compare, when specific benchmarks for programs you want to run aren't available.

Three weeks to one month from now, AMD's new Fusion APUs will start showing up in new mobile computer products, and for the same cost or less, than a system with an Intel CPU and Intel chipset video chip, will have a greatly enhanced graphics capability, with a game-capable version costing less than specifying a discrete card in an Intel based mobile computing system.

this information you have received thus far is not entirely true. you CAN replace/change video cards, CPUs, ram in laptops. it is just difficult and you must also contact your manufacturer first and ask them what upgrades may be available. CPU upgrades are probably more so.

It's been YEARS now since the last laptop producers offered upgrades of either a CPU or a GPU. The last such upgrades were quite expensive, involving the exchange of the entire mainboard, and exceeding the cost of a Netbook today. It became economically a poor value before that, of course.

^This

Alienware offered very limited upgrades (basically if they sold a model with three different cards and you bought the cheap one, you could buy the expensive one later on) that cost more than buying a new laptop. In the past, some laptop users had limited success in taking a certain model and inserting a better card from a different model which often required modify the cooling system. Not for the faint of heart. And the only place to get the spare card was second hand for once again almost the cost of a new laptop.

So basically, unfortunately, you're stuck with what you have. Most cards, even ATI ones, are integrated anyways. The non-intel integrated solutions will be able to play FONV if you lower the settings but the Intels not so much

The best laptop video cards are equivilent to mainstream desktop cards (meaning the $150-$200 range which isn't the high end) and are only available in larger configurations due to the heating/power requirements. That's not to say they aren't any good though, the best laptop cards can easily play modern games at high resolutions and framerates just fine. But desktops can go even higher, you just can't take them with you. The best bang for your buck are the Asus G53 and G73 republic of gamers series. They come equipped with an nvidia gtx 460m which is the equivilent of a desktop gts 450 in terms of power. The older version of the g73 has an ati 5870 and can be found for less. It's equivalent in performance to the 460m (has a higher 3dmark score because of the texture optimizations in use, but game fps are pretty much the same) but runs much hotter. You can probably get in cheaper though. Again, the performance is somewhere in between a 5750-5770 with dx11 support, not the equivalent of 5870 desktop card.