The Gt240 ddr5 its an old card, older than the HD5570, but the nVidia card is faster, I would suggest you a 440 gddr5 or something like that, also a 5670 gddr5 would be one of the best choice you can get for light gaming...
If you cant find anything better than that, get the gt240, i got an old build with an athlon ii x2 @3,0ghz, 4gb ram and that card, and runs almost all games in a 1440x900 resolution with high detail, which is more than enough for my little brother to play with better quality than my ps3 lol