unless you have an alienware laptop, i think your out of luck. ive never seen an upgrade video card for a laptop, except for alienware, and those are incredibly expensive.
this probably isnt what you were looking for, but this is the only kind of laptop i have seen that can have upgradeable memory.
what kind of connection in your laptop does the video card use. can it be removed? if you know the name of the connector, try googling that along with the type of card you are looking for.
in my mind the power requirements of these new cards just make it seem hard to use them on a laptop.
also even if you are able to find one, it may not even be able to connect to the display in the laptop. lets say you manage to find a card in the mini pci format which would plug into the minipci slot in the laptop. there would be no connection from the laptop's display to the new video card.
in any even here is the link to the alienware cards, these work becasue their laptops(i think) have a propitary connector that is basically an agp slot. in my laptop the agp is integrated fully into the motherboard, with no room for upgrade.
they are hiding from me right now, but they are located somewhere in the "gear shop"
here.