First the videcard that you have is Direcx9 compatible, meaning that it should be able to run the game. Maybe with some features turned off, like High Dynamic Range (HDR) or lowering a bit the detail level. Even if your video card wasn't DX9 compatible, it would just fall to software rendering on not hardware supported features.
So play this game and see if the performance is acceptable for you. If it isn't then buy the videocard, but at least give your computer a chance!
