|"i feel like this should be enough but it has a lousy frame rate"|
Define "lousy frame rate". Check the Game Benchmarks at the following link. For GTA4, they list 40-50's with the game settings on low or medium. When set to high, the FPS drop below 30.
We also have no idea how your system is configured or what programs you have installed. Did you dump all the crappy HP software? Are you running a lightweight anti-virus (not Norton or McAfee)? Have you managed your startup apps so that they don't suck the life out of your system? Have you tweaked Win7 for best performance?