GTA IV will not run well on anything less than an Intel Pentium D, because of the Cache size being too low.
To Run it you would need at Least:
For Low Graphics, No Lag: - Intel Pentium D 3.20GHz / Intel Core Duo (Not Core 2 Duo, This came out Later)
- 3GB DDR2 667MHz Ram. Slower Ram (ie. DDR 333 will reduce performance)
- You NEED Windows XP Service Pack 3 or Vista Service Pack 1.
Don't use Service Pack Mods, you wont get the fixes that the game needs.
- At Least an NVIDIA GEFORCE 8800GT 512Mb or ATI Radeon HD 3650 512Mb
For High Graphics, Maybe a Little Lag: - Intel Core 2 Extreme 3.0GHz / Intel Core i7
- 4GB DDR2 800MHz Ram (x86) or 8GB DDR2 800MHz Ram (x64)
- Windows 7 RTM. GTA IV is NOT Supported in Beta/RC Versions of 7.
- NVIDIA GEFORCE GTX260 896Mb or ATI Radeon HD 4890 X2 (2x1GB)
For Single PCI-E Slot Motherboards, 1 Radeon HD 4890 is fine.
Just Remember, Its Not all about The CPU Clock Speed or Graphics Card Memory Amount. You have to look at Cache Size, Front Side Bus Speed, GPU Clock, VRAM Clock and all that sort of stuff. Basically, if you want to run a new game really well, you need new hardware, not Hardware 6 or 12 months old.
For Those Posting Specifications in the Future, This Template should help you get them Right.
CPU Clock Speed: (Gigahertz / GHz)
RAM Speed: (MHz)
Graphics Card Type: (AGP/PCI-E 1.0/PCI-E 2.0)
Graphics Card Name:
Motherboard Graphics Interface: (PCI-E 1.0/PCI-E 2.0/AGP)
For Example, I'll fill it out
CPU Name: Intel Pentium D
CPU Clock Speed: 2.80GHz
Cores: 2 (Dual Core)
RAM Type: DDR2
RAM Speed: 800MHz (Megahertz)
RAM Amount: 4.0GB (Gigabytes)
Operating System: Windows XP Professional
Service Pack: Service Pack 3
Graphics Card Type: PCI-E 2.0
Graphics Card Name: NVIDIA GEFORCE 9600GSO
Graphics Memory: 384MB (Megabytes) Dedicated
Motherboard Type: ASUS P5QL Pro
Motherboard Graphics Interface: PCI-E 1.0
These are my Work PC's Specs. As you should be able to tell, it will not Run GTA IV very well due to the Old Processor and Low End Graphics Card.
A Program called "Everest Home Edition" will tell you all of these details. It comes as a free 30 day trial, more time than you need.
*Please Note: These Details are General Advice Only. Some People May Experience Poor Gameplay on Expensive Hardware or Good Gameplay on Cheap Hardware. I am NOT responsible for what you do with this Information.
Hope I have Helped. At lease use the Specifications Template above so that other people can help you more.