Can anybody help me out with this??

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I bought my pc about 1 years ago. That time I spent about $730 or 35000 INR. It has:- -dual core 2 processor 4300 @ 1.80 GHz - 1GB Ram -the motherborard is Intel G965 express chipset family, and -OS installed is Windows Xp professional. I want to play some advanced games involving quality graphics like GTA San andreas, Fifa 08, Gears of War etc. I have only GTA San andreas installed in my PC , but the problem is the while I play, the motion of the game is not very fluent, I contacted a computer retailer about the problem, he suggested me to install a Graphics card which ranges from $100-$350 and even more, but I don't want to spend so much amount of money only for games and moreover I don't have any idea about the Graphic cards and which to buy and which not, etc. Guys, is there any software which could help me in this , any tweaks, etc. ?? Is there any other alternative to buying an expensive graphics card, if not , which graphics card should I buy which would be both economical and very usefull for all games. ??