that's only one core, and GTAIV runs like sh*te on one core. (it isn't designed for them)
upgrade to a dual core or quad core CPU and you'll see
edit: holy shit, what made you think that the PC was good? it has a x4500... :/ good luck running games on that. (you might get some games to run, but your processor should be atleast dual core)
edit2: nevermind, I searched on the intel website and your processor is actually a dual core.
it's your epic failing graphic card (if you can even call it one) that stops you from playing GTAIV.