Looking at the system requirements here:http://support.rockstargames.com/entries/479435-PC-System-Requirements-for-GTA-IV
It actually would appear that a GT 630 would meet or exceed the recommended requirements. I would recommend a little more horsepower if you would play any newer games, however.
Tom's has a great list of graphics cards, from which I would recommend something more toward an AMD HD 7770, if you want great performance for not much more than the GT 630. You can compare graphics card value here:http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107-7.html
This is the card I'm recommending:http://www.newegg.com/Product/Product.aspx?Item=N82E16814202011