Recommended System Requirements for GTA IV:
OS: Windows Vista SP 1 or XP with SP 3
Processor: Intel Core 2 Quad 2.4Ghz, AMD Phenom X3 2.1Ghz
Memory: 2 GB (Windows XP) 2.5 GB (Windows Vista)
18 GB Free Hard Drive Space
Graphics/Video Card: 512MB NVIDIA 8600 / 512MB ATI 3870

Minimum System Requirements for GTA IV:
OS: Windows Vista SP1 / XP with SP3
Processor: Intel Core 2 Duo 1.8Ghz, AMD Athlon X2 64 2.4Ghz
Memory: 1.5GB
16GB Free Hard Drive Space
Graphics/Video Card: 256MB NVIDIA 7900 / 256MB ATI X1900