Can I upgrade video card for Acer Aspire 5520-5912 from GeForce 7000(an integrated card) to GeForce 8600 GT?

You cant install a video card in a notebook PC. You need to buy a high end laptop with a video card already installed from like Alienware or a Dell XPS M1710. Its not like a desktop where just about any PC will work with just about any video card. Most laptops(like yours) have onboard video chipsets. Only high end laptops have an actual video card & even then they cant be upgraded to a differant card.