Ok. Your graphics card is low-end. Im not sure it even passes the minimum...
Put everything on low.
Your processor's clock speed is pretty slow for games like GTA IV. As you are using Windows Vista, I would suggest closing litterally EVERYTHING when you play. MSN, Yahoo, Aim, SKype, Xfire, Torrent clients, Steam, THE LOT.
Apart from that, I would suggest upgrading to a better system
- Tom