If that is indeed a PCI video card, your options for upgrading will be very limited. Your CPU is just fine though.
Sl has had a bug for the past few months that make the 4xx series of cards crash on anything higher than medium graphic settings.
With the rate LL moves, it may be years before it is ever fixed. I have a GTX 460 that used to be great but now I have to default to medium graphics because it will crash as soon as I launch the game.