I looked at specs online and it's not very telling (I mean, the GT 220 has a higher clock rate than a [significantly faster] GT 240?). Other people who are asking the same question are usually hit with an advice to buy something else, instead of a good answer to the question.
Just to give you an idea of my expectations - my current rig has a 9500 GT, and it was enough for the kind of games I play (1024x768 is usually enough for me). But it would be nice if a 4650 or a gt 220 would give me more FPS.
Off topic rant: it kinda irks me that the the progression of videocards nowadays is not "newer model is faster than the previous generation's" but "current model of a card is roughly equal to previous generation's equivalent, and then you use the 2nd digit to decide which of the current generation is faster".
I could understand it with rebrands, but a GT 430 being slower than a card that is two generations of architecture older (9600 GT)? I mean, the 8800 GTS is still a viable high end card these days.
Back in the day, when faced with an FX 5500, a geforce 6200 and a 7300 GT, you'll automatically know which one is faster just based on their generation and their overall model number.