is your gcard memory shared?
i think most all laptop cards are that are just express u have to have either a mobility radeon or geforce go series to actually have independent ram larger than 64mb
OC'ing and laptop cards is a serious bad idea just like integrated gfx on desktops you run the risk of frying your mobo and chipset not just the gfx card since the integrated gfx are usually on the same chip as the northbridge or southbridge to my knowledge
also laptops to my knowledge are specifically engineered to only provide so much power to things so uping you speed could put additional draw on your laptops power and cause something else to fry no to mention laptops are not well known for there heat dissipation and cooling performance and since u have no temperature monitoring on your chip you may not know if you pushing over its bounds to much heat don't all ways = artifacts
