I have the same video card as yours, and I've been considering on replacing it for a while now. It doesn't have Pixel Shader feature, so lots of modern games can't run with it (i.e Black & White 2, Fable 2), and resource greedy games like FEAR, Doom 3, Quake 4 never get enough FPS to be played, even in lowest settings.
512 RAM is the minimum for game and picture/video editing right now, so u may want to add another 512.
If u don't use ur system for gaming or heavy calculation/rendering, and if everything still works well, my advice is to invest ur money in a good monitor, mouse & keyboard, spacey hard drive, and a UPS.