I too also have a laptop which does'nt allow me to play any kind of graphically challenging game. This is why i have my desktop. As for upgrading your graphics card it's just not possible in a laptop as i'm sure there integrated onto the motherboard. The only part i know of that's upgradeable on a laptop is the memory, howver you may have reached your max at 512, you'd have to check the manuals which you don't have and i can't find anywhere on the net.
With regards to the graphics card i have always prefered radeon cards, no particular reason.