It would be incorrect to say that you "cant" play GTAIV on your PC. 'Playing' and 'playable' are two different things. WShile you may be able to 'play' the game on your setup, it won't be 'playable', i.e, you'll be getting way low FPS. Keep in mind that GTAIV is really heavy on the CPU, not so much on the GPU. Since your CPU is running @3Ghz, it won't give you 'playable' FPS.