You'd need a decent quad core that has a good clock rate. Like at least 2.8GHz or high. and you'd have to have a video card with a lot of vram. Like a Radeon 4890 2GB version, or a GTX 285 2GB version.
--- Dell Studio XPS | Radeon 4850 | 640GB HD | 4GB DDR3 RAM | i7 2.66 GHz it's so easy to edit your post with Gamefox, total fail on your part. -xerotonine
Even though I have an Ati GPU, the Radeon 4890 2GB is poor with the 1GB frame buffer whereas the recent Nvidia GPUs are ideal for xtreme resolutions. If you want max settings ingame, the game will want to use around 1600MB VRAM so don't skimp if you want the game looking its best and use SLI.
To overide game enforcement to set what gfx setting you desire, create a shortcut of LaunchGTAIV.exe to your desktop and the Target location should look like Rockstar Games\Grand Theft Auto IV\LaunchGTAIV.exe" -norestrictions