I beg to differ. I am running an Intel E6300 and nVidea 9600GT with 4GB DDR2 RAM. I CAN run GTA 4 on medium settings.
Yeah, but the 8600 is what he's running as far as a GPU. The 9600 is better so it's probably helping but still, a quad core will get you the best performance. I'm not saying it's absolutely necessary, but it does help. GTA IV has been programmed to take advantage of CPUs with 3 or 4 cores.