No, first of all, it would be very hard to get the card out of the Xbox in the first place. Second of all, laptop cards are pretty specialized things so it probably wouldn't be compatible even if you did SOMEHOW get it out of the Xbox without damaging it. And third of all. The Xbox graphics card actually isn't that powerful, so it's really not worth all the trouble.
P.S. I'm an Xbox fanboy myself, but I have to admit the PS3 has a better graphics card.