Unfortunately, you can't buy graphic cards for notebooks. They use integrated chips, instead, which saves space. The only upgradeable video system that I know of is by Alienware...but their laptops are expensive. Simply put, you'll have to stay with what you get.
This doesn't have anything to do with this, but are the same David that asked us to donate money, because you needed money to support your kids or something? I'm sorry if I have the wrong person, but your screenname strikes something in my memory...