It will run, but it will be unplayable with your current system specs. GTA IV is extremely different to run (console port, bad encoding, etc.). You really need a strong quad core (you can slide with a strong dual core) with a decent graphics card to get the game to run smoothly (25 to 30FPS).
You can expect around 13-20 Frames Per second with that setup. The game will be playable but it will look choppy and you will experience some lag. It will play the older Grand Theft Auto: San Andreas perfectly though. If You haven't already played Grand Theft Auto: San Andreas then I suggest you give it a look.