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.