The requirements for the PC version of Grand Theft Auto IV have been revealed by IGN. As you'll soon see, the recommended specs certainly weren't far off the mark of those shown on the Games for Windows site a while back.
The IGN article also confirms that the game has been delayed until December. That places it at just a few weeks later than expected.
Source
Minimum System Requirements
* OS: Windows Vista - Service Pack 1 / XP - Service Pack 3
* Processor: Intel Core 2 Duo 1.8Ghz, AMD Athlon X2 64 2.4Ghz
* Memory: 1.5GB, 16GB Free Hard Drive Space
* Video Card: 256MB NVIDIA 7900 / 256MB ATI X1900
Recommended System Requirements
* OS: Windows Vista - Service Pack 1 / XP - Service Pack 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
* Video Card: 512MB NVIDIA 8600 / 512MB ATI 3870
* OS: Windows Vista - Service Pack 1 / XP - Service Pack 3
* Processor: Intel Core 2 Duo 1.8Ghz, AMD Athlon X2 64 2.4Ghz
* Memory: 1.5GB, 16GB Free Hard Drive Space
* Video Card: 256MB NVIDIA 7900 / 256MB ATI X1900
Recommended System Requirements
* OS: Windows Vista - Service Pack 1 / XP - Service Pack 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
* Video Card: 512MB NVIDIA 8600 / 512MB ATI 3870
The IGN article also confirms that the game has been delayed until December. That places it at just a few weeks later than expected.
Source