Only about ~5% of laptops have a seperate video "card" but even then a replacement card has to fix and be compatible (thermal output, shape/size, power requirements etc).
From experiece Acer, Toshiba and Dell are the most common to have seperate cards.
I have torn apart an old Acer to remove the failed Nvidia card out and replaced it with an ATi based card (from another unit that had died) and it did work but you get weird anomalies like no gpu temps, issues detecting exactly what gpu/specs etc but as far as 3D games and applications and drivers it was AOK.
I wouldnt bother seriously.