Its generally impossible to change video cards in laptops as most of the time theyre soldered onto the motherboard, if not laptop cards are very hard to find... better off getting a new laptop with better graphics
I'm gonna have to say no. If you do not want to buy a new laptop, then you may be interested in shuttles initiative to allow you to build your own laptop. You'd still have to buy the motherboard, screen, casing, and keyboard, but you could use the CPU, RAM, and Drives from your current Acer. Well, so long as you don't mind putting together a really small and delicate system ^_^
:S ..... dedicated grafix card!?!?!?! if its dedicated @ 256MB then thats the highest you'll see - overclocking your graphics card isnt an option, you'll just fry the chip in doing so. If it were hyper memory, you could've increased your overall ram to notice an increase in graphics memory.