I don't think graphic card is that big a deal, it's mostly a matter of how high you can push the detail settings.
Now the MOST important thing is to have enough RAM, I think that 1.25GB should be enough, but you can check task manager to see if your system has spare memory while running CIV. If the system starts thrashing (accessing the harddrive) then performance goes to hell, 2GB ram is always good - but basically you either have enough or you don't.
The faster the CPU, the better. It's as simple as that, if your CPU is twice as fast, then the in between turns takes half as long. CIV benefits surprisingly from a dual core processor, it's not designed to but it does. A modern CPU would be 10x faster than your current one but I suspect the notebook would have poor upgradeability in the CPU department (ie you'd need a new system to realize significant benefits).